Issue #6215: backport the 3.1 io lib

1 files changed, 1962 insertions, 0 deletions

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
new file mode 100644
index 0000000..5f18b12
--- /dev/null
+++ b/Lib/_pyio.py
@@ -0,0 +1,1962 @@
+"""
+Python implementation of the io module.
+"""
+
+from __future__ import print_function
+from __future__ import unicode_literals
+
+import os
+import abc
+import codecs
+import warnings
+# Import _thread instead of threading to reduce startup cost
+try:
+    from thread import allocate_lock as Lock
+except ImportError:
+    from dummy_thread import allocate_lock as Lock
+
+import io
+from io import __all__
+from io import SEEK_SET, SEEK_CUR, SEEK_END
+
+__metaclass__ = type
+
+# open() uses st_blksize whenever we can
+DEFAULT_BUFFER_SIZE = 8 * 1024  # bytes
+
+# NOTE: Base classes defined here are registered with the "official" ABCs
+# defined in io.py. We don't use real inheritance though, because we don't
+# want to inherit the C implementations.
+
+
+class BlockingIOError(IOError):
+
+    """Exception raised when I/O would block on a non-blocking I/O stream."""
+
+    def __init__(self, errno, strerror, characters_written=0):
+        super(IOError, self).__init__(errno, strerror)
+        if not isinstance(characters_written, (int, long)):
+            raise TypeError("characters_written must be a integer")
+        self.characters_written = characters_written
+
+
+def open(file, mode="r", buffering=None,
+         encoding=None, errors=None,
+         newline=None, closefd=True):
+
+    r"""Open file and return a stream.  Raise IOError upon failure.
+
+    file is either a text or byte string giving the name (and the path
+    if the file isn't in the current working directory) of the file to
+    be opened or an integer file descriptor of the file to be
+    wrapped. (If a file descriptor is given, it is closed when the
+    returned I/O object is closed, unless closefd is set to False.)
+
+    mode is an optional string that specifies the mode in which the file
+    is opened. It defaults to 'r' which means open for reading in text
+    mode.  Other common values are 'w' for writing (truncating the file if
+    it already exists), and 'a' for appending (which on some Unix systems,
+    means that all writes append to the end of the file regardless of the
+    current seek position). In text mode, if encoding is not specified the
+    encoding used is platform dependent. (For reading and writing raw
+    bytes use binary mode and leave encoding unspecified.) The available
+    modes are:
+
+    ========= ===============================================================
+    Character Meaning
+    --------- ---------------------------------------------------------------
+    'r'       open for reading (default)
+    'w'       open for writing, truncating the file first
+    'a'       open for writing, appending to the end of the file if it exists
+    'b'       binary mode
+    't'       text mode (default)
+    '+'       open a disk file for updating (reading and writing)
+    'U'       universal newline mode (for backwards compatibility; unneeded
+              for new code)
+    ========= ===============================================================
+
+    The default mode is 'rt' (open for reading text). For binary random
+    access, the mode 'w+b' opens and truncates the file to 0 bytes, while
+    'r+b' opens the file without truncation.
+
+    Python distinguishes between files opened in binary and text modes,
+    even when the underlying operating system doesn't. Files opened in
+    binary mode (appending 'b' to the mode argument) return contents as
+    bytes objects without any decoding. In text mode (the default, or when
+    't' is appended to the mode argument), the contents of the file are
+    returned as strings, the bytes having been first decoded using a
+    platform-dependent encoding or using the specified encoding if given.
+
+    buffering is an optional integer used to set the buffering policy. By
+    default full buffering is on. Pass 0 to switch buffering off (only
+    allowed in binary mode), 1 to set line buffering, and an integer > 1
+    for full buffering.
+
+    encoding is the name of the encoding used to decode or encode the
+    file. This should only be used in text mode. The default encoding is
+    platform dependent, but any encoding supported by Python can be
+    passed.  See the codecs module for the list of supported encodings.
+
+    errors is an optional string that specifies how encoding errors are to
+    be handled---this argument should not be used in binary mode. Pass
+    'strict' to raise a ValueError exception if there is an encoding error
+    (the default of None has the same effect), or pass 'ignore' to ignore
+    errors. (Note that ignoring encoding errors can lead to data loss.)
+    See the documentation for codecs.register for a list of the permitted
+    encoding error strings.
+
+    newline controls how universal newlines works (it only applies to text
+    mode). It can be None, '', '\n', '\r', and '\r\n'.  It works as
+    follows:
+
+    * On input, if newline is None, universal newlines mode is
+      enabled. Lines in the input can end in '\n', '\r', or '\r\n', and
+      these are translated into '\n' before being returned to the
+      caller. If it is '', universal newline mode is enabled, but line
+      endings are returned to the caller untranslated. If it has any of
+      the other legal values, input lines are only terminated by the given
+      string, and the line ending is returned to the caller untranslated.
+
+    * On output, if newline is None, any '\n' characters written are
+      translated to the system default line separator, os.linesep. If
+      newline is '', no translation takes place. If newline is any of the
+      other legal values, any '\n' characters written are translated to
+      the given string.
+
+    If closefd is False, the underlying file descriptor will be kept open
+    when the file is closed. This does not work when a file name is given
+    and must be True in that case.
+
+    open() returns a file object whose type depends on the mode, and
+    through which the standard file operations such as reading and writing
+    are performed. When open() is used to open a file in a text mode ('w',
+    'r', 'wt', 'rt', etc.), it returns a TextIOWrapper. When used to open
+    a file in a binary mode, the returned class varies: in read binary
+    mode, it returns a BufferedReader; in write binary and append binary
+    modes, it returns a BufferedWriter, and in read/write mode, it returns
+    a BufferedRandom.
+
+    It is also possible to use a string or bytearray as a file for both
+    reading and writing. For strings StringIO can be used like a file
+    opened in a text mode, and for bytes a BytesIO can be used like a file
+    opened in a binary mode.
+    """
+    if not isinstance(file, (basestring, int, long)):
+        raise TypeError("invalid file: %r" % file)
+    if not isinstance(mode, basestring):
+        raise TypeError("invalid mode: %r" % mode)
+    if buffering is not None and not isinstance(buffering, (int, long)):
+        raise TypeError("invalid buffering: %r" % buffering)
+    if encoding is not None and not isinstance(encoding, basestring):
+        raise TypeError("invalid encoding: %r" % encoding)
+    if errors is not None and not isinstance(errors, basestring):
+        raise TypeError("invalid errors: %r" % errors)
+    modes = set(mode)
+    if modes - set("arwb+tU") or len(mode) > len(modes):
+        raise ValueError("invalid mode: %r" % mode)
+    reading = "r" in modes
+    writing = "w" in modes
+    appending = "a" in modes
+    updating = "+" in modes
+    text = "t" in modes
+    binary = "b" in modes
+    if "U" in modes:
+        if writing or appending:
+            raise ValueError("can't use U and writing mode at once")
+        reading = True
+    if text and binary:
+        raise ValueError("can't have text and binary mode at once")
+    if reading + writing + appending > 1:
+        raise ValueError("can't have read/write/append mode at once")
+    if not (reading or writing or appending):
+        raise ValueError("must have exactly one of read/write/append mode")
+    if binary and encoding is not None:
+        raise ValueError("binary mode doesn't take an encoding argument")
+    if binary and errors is not None:
+        raise ValueError("binary mode doesn't take an errors argument")
+    if binary and newline is not None:
+        raise ValueError("binary mode doesn't take a newline argument")
+    raw = FileIO(file,
+                 (reading and "r" or "") +
+                 (writing and "w" or "") +
+                 (appending and "a" or "") +
+                 (updating and "+" or ""),
+                 closefd)
+    if buffering is None:
+        buffering = -1
+    line_buffering = False
+    if buffering == 1 or buffering < 0 and raw.isatty():
+        buffering = -1
+        line_buffering = True
+    if buffering < 0:
+        buffering = DEFAULT_BUFFER_SIZE
+        try:
+            bs = os.fstat(raw.fileno()).st_blksize
+        except (os.error, AttributeError):
+            pass
+        else:
+            if bs > 1:
+                buffering = bs
+    if buffering < 0:
+        raise ValueError("invalid buffering size")
+    if buffering == 0:
+        if binary:
+            return raw
+        raise ValueError("can't have unbuffered text I/O")
+    if updating:
+        buffer = BufferedRandom(raw, buffering)
+    elif writing or appending:
+        buffer = BufferedWriter(raw, buffering)
+    elif reading:
+        buffer = BufferedReader(raw, buffering)
+    else:
+        raise ValueError("unknown mode: %r" % mode)
+    if binary:
+        return buffer
+    text = TextIOWrapper(buffer, encoding, errors, newline, line_buffering)
+    text.mode = mode
+    return text
+
+
+class DocDescriptor:
+    """Helper for builtins.open.__doc__
+    """
+    def __get__(self, obj, typ):
+        return (
+            "open(file, mode='r', buffering=None, encoding=None, "
+                 "errors=None, newline=None, closefd=True)\n\n" +
+            open.__doc__)
+
+class OpenWrapper:
+    """Wrapper for builtins.open
+
+    Trick so that open won't become a bound method when stored
+    as a class variable (as dbm.dumb does).
+
+    See initstdio() in Python/pythonrun.c.
+    """
+    __doc__ = DocDescriptor()
+
+    def __new__(cls, *args, **kwargs):
+        return open(*args, **kwargs)
+
+
+class UnsupportedOperation(ValueError, IOError):
+    pass
+
+
+class IOBase:
+    __metaclass__ = abc.ABCMeta
+
+    """The abstract base class for all I/O classes, acting on streams of
+    bytes. There is no public constructor.
+
+    This class provides dummy implementations for many methods that
+    derived classes can override selectively; the default implementations
+    represent a file that cannot be read, written or seeked.
+
+    Even though IOBase does not declare read, readinto, or write because
+    their signatures will vary, implementations and clients should
+    consider those methods part of the interface. Also, implementations
+    may raise a IOError when operations they do not support are called.
+
+    The basic type used for binary data read from or written to a file is
+    bytes. bytearrays are accepted too, and in some cases (such as
+    readinto) needed. Text I/O classes work with str data.
+
+    Note that calling any method (even inquiries) on a closed stream is
+    undefined. Implementations may raise IOError in this case.
+
+    IOBase (and its subclasses) support the iterator protocol, meaning
+    that an IOBase object can be iterated over yielding the lines in a
+    stream.
+
+    IOBase also supports the :keyword:`with` statement. In this example,
+    fp is closed after the suite of the with statement is complete:
+
+    with open('spam.txt', 'r') as fp:
+        fp.write('Spam and eggs!')
+    """
+
+    ### Internal ###
+
+    def _unsupported(self, name):
+        """Internal: raise an exception for unsupported operations."""
+        raise UnsupportedOperation("%s.%s() not supported" %
+                                   (self.__class__.__name__, name))
+
+    ### Positioning ###
+
+    def seek(self, pos, whence=0):
+        """Change stream position.
+
+        Change the stream position to byte offset offset. offset is
+        interpreted relative to the position indicated by whence.  Values
+        for whence are:
+
+        * 0 -- start of stream (the default); offset should be zero or positive
+        * 1 -- current stream position; offset may be negative
+        * 2 -- end of stream; offset is usually negative
+
+        Return the new absolute position.
+        """
+        self._unsupported("seek")
+
+    def tell(self):
+        """Return current stream position."""
+        return self.seek(0, 1)
+
+    def truncate(self, pos=None):
+        """Truncate file to size bytes.
+
+        Size defaults to the current IO position as reported by tell().  Return
+        the new size.
+        """
+        self._unsupported("truncate")
+
+    ### Flush and close ###
+
+    def flush(self):
+        """Flush write buffers, if applicable.
+
+        This is not implemented for read-only and non-blocking streams.
+        """
+        # XXX Should this return the number of bytes written???
+
+    __closed = False
+
+    def close(self):
+        """Flush and close the IO object.
+
+        This method has no effect if the file is already closed.
+        """
+        if not self.__closed:
+            try:
+                self.flush()
+            except IOError:
+                pass  # If flush() fails, just give up
+            self.__closed = True
+
+    def __del__(self):
+        """Destructor.  Calls close()."""
+        # The try/except block is in case this is called at program
+        # exit time, when it's possible that globals have already been
+        # deleted, and then the close() call might fail.  Since
+        # there's nothing we can do about such failures and they annoy
+        # the end users, we suppress the traceback.
+        try:
+            self.close()
+        except:
+            pass
+
+    ### Inquiries ###
+
+    def seekable(self):
+        """Return whether object supports random access.
+
+        If False, seek(), tell() and truncate() will raise IOError.
+        This method may need to do a test seek().
+        """
+        return False
+
+    def _checkSeekable(self, msg=None):
+        """Internal: raise an IOError if file is not seekable
+        """
+        if not self.seekable():
+            raise IOError("File or stream is not seekable."
+                          if msg is None else msg)
+
+
+    def readable(self):
+        """Return whether object was opened for reading.
+
+        If False, read() will raise IOError.
+        """
+        return False
+
+    def _checkReadable(self, msg=None):
+        """Internal: raise an IOError if file is not readable
+        """
+        if not self.readable():
+            raise IOError("File or stream is not readable."
+                          if msg is None else msg)
+
+    def writable(self):
+        """Return whether object was opened for writing.
+
+        If False, write() and truncate() will raise IOError.
+        """
+        return False
+
+    def _checkWritable(self, msg=None):
+        """Internal: raise an IOError if file is not writable
+        """
+        if not self.writable():
+            raise IOError("File or stream is not writable."
+                          if msg is None else msg)
+
+    @property
+    def closed(self):
+        """closed: bool.  True iff the file has been closed.
+
+        For backwards compatibility, this is a property, not a predicate.
+        """
+        return self.__closed
+
+    def _checkClosed(self, msg=None):
+        """Internal: raise an ValueError if file is closed
+        """
+        if self.closed:
+            raise ValueError("I/O operation on closed file."
+                             if msg is None else msg)
+
+    ### Context manager ###
+
+    def __enter__(self):
+        """Context management protocol.  Returns self."""
+        self._checkClosed()
+        return self
+
+    def __exit__(self, *args):
+        """Context management protocol.  Calls close()"""
+        self.close()
+
+    ### Lower-level APIs ###
+
+    # XXX Should these be present even if unimplemented?
+
+    def fileno(self):
+        """Returns underlying file descriptor if one exists.
+
+        An IOError is raised if the IO object does not use a file descriptor.
+        """
+        self._unsupported("fileno")
+
+    def isatty(self):
+        """Return whether this is an 'interactive' stream.
+
+        Return False if it can't be determined.
+        """
+        self._checkClosed()
+        return False
+
+    ### Readline[s] and writelines ###
+
+    def readline(self, limit=-1):
+        r"""Read and return a line from the stream.
+
+        If limit is specified, at most limit bytes will be read.
+
+        The line terminator is always b'\n' for binary files; for text
+        files, the newlines argument to open can be used to select the line
+        terminator(s) recognized.
+        """
+        # For backwards compatibility, a (slowish) readline().
+        if hasattr(self, "peek"):
+            def nreadahead():
+                readahead = self.peek(1)
+                if not readahead:
+                    return 1
+                n = (readahead.find(b"\n") + 1) or len(readahead)
+                if limit >= 0:
+                    n = min(n, limit)
+                return n
+        else:
+            def nreadahead():
+                return 1
+        if limit is None:
+            limit = -1
+        elif not isinstance(limit, (int, long)):
+            raise TypeError("limit must be an integer")
+        res = bytearray()
+        while limit < 0 or len(res) < limit:
+            b = self.read(nreadahead())
+            if not b:
+                break
+            res += b
+            if res.endswith(b"\n"):
+                break
+        return bytes(res)
+
+    def __iter__(self):
+        self._checkClosed()
+        return self
+
+    def next(self):
+        line = self.readline()
+        if not line:
+            raise StopIteration
+        return line
+
+    def readlines(self, hint=None):
+        """Return a list of lines from the stream.
+
+        hint can be specified to control the number of lines read: no more
+        lines will be read if the total size (in bytes/characters) of all
+        lines so far exceeds hint.
+        """
+        if hint is not None and not isinstance(hint, (int, long)):
+            raise TypeError("integer or None expected")
+        if hint is None or hint <= 0:
+            return list(self)
+        n = 0
+        lines = []
+        for line in self:
+            lines.append(line)
+            n += len(line)
+            if n >= hint:
+                break
+        return lines
+
+    def writelines(self, lines):
+        self._checkClosed()
+        for line in lines:
+            self.write(line)
+
+io.IOBase.register(IOBase)
+
+
+class RawIOBase(IOBase):
+
+    """Base class for raw binary I/O."""
+
+    # The read() method is implemented by calling readinto(); derived
+    # classes that want to support read() only need to implement
+    # readinto() as a primitive operation.  In general, readinto() can be
+    # more efficient than read().
+
+    # (It would be tempting to also provide an implementation of
+    # readinto() in terms of read(), in case the latter is a more suitable
+    # primitive operation, but that would lead to nasty recursion in case
+    # a subclass doesn't implement either.)
+
+    def read(self, n=-1):
+        """Read and return up to n bytes.
+
+        Returns an empty bytes object on EOF, or None if the object is
+        set not to block and has no data to read.
+        """
+        if n is None:
+            n = -1
+        if n < 0:
+            return self.readall()
+        b = bytearray(n.__index__())
+        n = self.readinto(b)
+        del b[n:]
+        return bytes(b)
+
+    def readall(self):
+        """Read until EOF, using multiple read() call."""
+        res = bytearray()
+        while True:
+            data = self.read(DEFAULT_BUFFER_SIZE)
+            if not data:
+                break
+            res += data
+        return bytes(res)
+
+    def readinto(self, b):
+        """Read up to len(b) bytes into b.
+
+        Returns number of bytes read (0 for EOF), or None if the object
+        is set not to block as has no data to read.
+        """
+        self._unsupported("readinto")
+
+    def write(self, b):
+        """Write the given buffer to the IO stream.
+
+        Returns the number of bytes written, which may be less than len(b).
+        """
+        self._unsupported("write")
+
+io.RawIOBase.register(RawIOBase)
+from _io import FileIO
+RawIOBase.register(FileIO)
+
+
+class BufferedIOBase(IOBase):
+
+    """Base class for buffered IO objects.
+
+    The main difference with RawIOBase is that the read() method
+    supports omitting the size argument, and does not have a default
+    implementation that defers to readinto().
+
+    In addition, read(), readinto() and write() may raise
+    BlockingIOError if the underlying raw stream is in non-blocking
+    mode and not ready; unlike their raw counterparts, they will never
+    return None.
+
+    A typical implementation should not inherit from a RawIOBase
+    implementation, but wrap one.
+    """
+
+    def read(self, n=None):
+        """Read and return up to n bytes.
+
+        If the argument is omitted, None, or negative, reads and
+        returns all data until EOF.
+
+        If the argument is positive, and the underlying raw stream is
+        not 'interactive', multiple raw reads may be issued to satisfy
+        the byte count (unless EOF is reached first).  But for
+        interactive raw streams (XXX and for pipes?), at most one raw
+        read will be issued, and a short result does not imply that
+        EOF is imminent.
+
+        Returns an empty bytes array on EOF.
+
+        Raises BlockingIOError if the underlying raw stream has no
+        data at the moment.
+        """
+        self._unsupported("read")
+
+    def read1(self, n=None):
+        """Read up to n bytes with at most one read() system call."""
+        self._unsupported("read1")
+
+    def readinto(self, b):
+        """Read up to len(b) bytes into b.
+
+        Like read(), this may issue multiple reads to the underlying raw
+        stream, unless the latter is 'interactive'.
+
+        Returns the number of bytes read (0 for EOF).
+
+        Raises BlockingIOError if the underlying raw stream has no
+        data at the moment.
+        """
+        # XXX This ought to work with anything that supports the buffer API
+        data = self.read(len(b))
+        n = len(data)
+        try:
+            b[:n] = data
+        except TypeError as err:
+            import array
+            if not isinstance(b, array.array):
+                raise err
+            b[:n] = array.array(b'b', data)
+        return n
+
+    def write(self, b):
+        """Write the given buffer to the IO stream.
+
+        Return the number of bytes written, which is never less than
+        len(b).
+
+        Raises BlockingIOError if the buffer is full and the
+        underlying raw stream cannot accept more data at the moment.
+        """
+        self._unsupported("write")
+
+    def detach(self):
+        """
+        Separate the underlying raw stream from the buffer and return it.
+
+        After the raw stream has been detached, the buffer is in an unusable
+        state.
+        """
+        self._unsupported("detach")
+
+io.BufferedIOBase.register(BufferedIOBase)
+
+
+class _BufferedIOMixin(BufferedIOBase):
+
+    """A mixin implementation of BufferedIOBase with an underlying raw stream.
+
+    This passes most requests on to the underlying raw stream.  It
+    does *not* provide implementations of read(), readinto() or
+    write().
+    """
+
+    def __init__(self, raw):
+        self.raw = raw
+
+    ### Positioning ###
+
+    def seek(self, pos, whence=0):
+        new_position = self.raw.seek(pos, whence)
+        if new_position < 0:
+            raise IOError("seek() returned an invalid position")
+        return new_position
+
+    def tell(self):
+        pos = self.raw.tell()
+        if pos < 0:
+            raise IOError("tell() returned an invalid position")
+        return pos
+
+    def truncate(self, pos=None):
+        # Flush the stream.  We're mixing buffered I/O with lower-level I/O,
+        # and a flush may be necessary to synch both views of the current
+        # file state.
+        self.flush()
+
+        if pos is None:
+            pos = self.tell()
+        # XXX: Should seek() be used, instead of passing the position
+        # XXX  directly to truncate?
+        return self.raw.truncate(pos)
+
+    ### Flush and close ###
+
+    def flush(self):
+        self.raw.flush()
+
+    def close(self):
+        if not self.closed and self.raw is not None:
+            try:
+                self.flush()
+            except IOError:
+                pass  # If flush() fails, just give up
+            self.raw.close()
+
+    def detach(self):
+        if self.raw is None:
+            raise ValueError("raw stream already detached")
+        self.flush()
+        raw = self.raw
+        self.raw = None
+        return raw
+
+    ### Inquiries ###
+
+    def seekable(self):
+        return self.raw.seekable()
+
+    def readable(self):
+        return self.raw.readable()
+
+    def writable(self):
+        return self.raw.writable()
+
+    @property
+    def closed(self):
+        return self.raw.closed
+
+    @property
+    def name(self):
+        return self.raw.name
+
+    @property
+    def mode(self):
+        return self.raw.mode
+
+    def __repr__(self):
+        clsname = self.__class__.__name__
+        try:
+            name = self.name
+        except AttributeError:
+            return "<_pyio.{0}>".format(clsname)
+        else:
+            return "<_pyio.{0} name={1!r}>".format(clsname, name)
+
+    ### Lower-level APIs ###
+
+    def fileno(self):
+        return self.raw.fileno()
+
+    def isatty(self):
+        return self.raw.isatty()
+
+
+class BytesIO(BufferedIOBase):
+
+    """Buffered I/O implementation using an in-memory bytes buffer."""
+
+    def __init__(self, initial_bytes=None):
+        buf = bytearray()
+        if initial_bytes is not None:
+            buf.extend(initial_bytes)
+        self._buffer = buf
+        self._pos = 0
+
+    def getvalue(self):
+        """Return the bytes value (contents) of the buffer
+        """
+        if self.closed:
+            raise ValueError("getvalue on closed file")
+        return bytes(self._buffer)
+
+    def read(self, n=None):
+        if self.closed:
+            raise ValueError("read from closed file")
+        if n is None:
+            n = -1
+        if not isinstance(n, (int, long)):
+            raise TypeError("integer argument expected, got {0!r}".format(
+                type(n)))
+        if n < 0:
+            n = len(self._buffer)
+        if len(self._buffer) <= self._pos:
+            return b""
+        newpos = min(len(self._buffer), self._pos + n)
+        b = self._buffer[self._pos : newpos]
+        self._pos = newpos
+        return bytes(b)
+
+    def read1(self, n):
+        """This is the same as read.
+        """
+        return self.read(n)
+
+    def write(self, b):
+        if self.closed:
+            raise ValueError("write to closed file")
+        if isinstance(b, unicode):
+            raise TypeError("can't write unicode to binary stream")
+        n = len(b)
+        if n == 0:
+            return 0
+        pos = self._pos
+        if pos > len(self._buffer):
+            # Inserts null bytes between the current end of the file
+            # and the new write position.
+            padding = b'\x00' * (pos - len(self._buffer))
+            self._buffer += padding
+        self._buffer[pos:pos + n] = b
+        self._pos += n
+        return n
+
+    def seek(self, pos, whence=0):
+        if self.closed:
+            raise ValueError("seek on closed file")
+        try:
+            pos = pos.__index__()
+        except AttributeError as err:
+            raise TypeError("an integer is required")
+        if whence == 0:
+            if pos < 0:
+                raise ValueError("negative seek position %r" % (pos,))
+            self._pos = pos
+        elif whence == 1:
+            self._pos = max(0, self._pos + pos)
+        elif whence == 2:
+            self._pos = max(0, len(self._buffer) + pos)
+        else:
+            raise ValueError("invalid whence value")
+        return self._pos
+
+    def tell(self):
+        if self.closed:
+            raise ValueError("tell on closed file")
+        return self._pos
+
+    def truncate(self, pos=None):
+        if self.closed:
+            raise ValueError("truncate on closed file")
+        if pos is None:
+            pos = self._pos
+        elif pos < 0:
+            raise ValueError("negative truncate position %r" % (pos,))
+        del self._buffer[pos:]
+        return self.seek(pos)
+
+    def readable(self):
+        return True
+
+    def writable(self):
+        return True
+
+    def seekable(self):
+        return True
+
+
+class BufferedReader(_BufferedIOMixin):
+
+    """BufferedReader(raw[, buffer_size])
+
+    A buffer for a readable, sequential BaseRawIO object.
+
+    The constructor creates a BufferedReader for the given readable raw
+    stream and buffer_size. If buffer_size is omitted, DEFAULT_BUFFER_SIZE
+    is used.
+    """
+
+    def __init__(self, raw, buffer_size=DEFAULT_BUFFER_SIZE):
+        """Create a new buffered reader using the given readable raw IO object.
+        """
+        if not raw.readable():
+            raise IOError('"raw" argument must be readable.')
+
+        _BufferedIOMixin.__init__(self, raw)
+        if buffer_size <= 0:
+            raise ValueError("invalid buffer size")
+        self.buffer_size = buffer_size
+        self._reset_read_buf()
+        self._read_lock = Lock()
+
+    def _reset_read_buf(self):
+        self._read_buf = b""
+        self._read_pos = 0
+
+    def read(self, n=None):
+        """Read n bytes.
+
+        Returns exactly n bytes of data unless the underlying raw IO
+        stream reaches EOF or if the call would block in non-blocking
+        mode. If n is negative, read until EOF or until read() would
+        block.
+        """
+        if n is not None and n < -1:
+            raise ValueError("invalid number of bytes to read")
+        with self._read_lock:
+            return self._read_unlocked(n)
+
+    def _read_unlocked(self, n=None):
+        nodata_val = b""
+        empty_values = (b"", None)
+        buf = self._read_buf
+        pos = self._read_pos
+
+        # Special case for when the number of bytes to read is unspecified.
+        if n is None or n == -1:
+            self._reset_read_buf()
+            chunks = [buf[pos:]]  # Strip the consumed bytes.
+            current_size = 0
+            while True:
+                # Read until EOF or until read() would block.
+                chunk = self.raw.read()
+                if chunk in empty_values:
+                    nodata_val = chunk
+                    break
+                current_size += len(chunk)
+                chunks.append(chunk)
+            return b"".join(chunks) or nodata_val
+
+        # The number of bytes to read is specified, return at most n bytes.
+        avail = len(buf) - pos  # Length of the available buffered data.
+        if n <= avail:
+            # Fast path: the data to read is fully buffered.
+            self._read_pos += n
+            return buf[pos:pos+n]
+        # Slow path: read from the stream until enough bytes are read,
+        # or until an EOF occurs or until read() would block.
+        chunks = [buf[pos:]]
+        wanted = max(self.buffer_size, n)
+        while avail < n:
+            chunk = self.raw.read(wanted)
+            if chunk in empty_values:
+                nodata_val = chunk
+                break
+            avail += len(chunk)
+            chunks.append(chunk)
+        # n is more then avail only when an EOF occurred or when
+        # read() would have blocked.
+        n = min(n, avail)
+        out = b"".join(chunks)
+        self._read_buf = out[n:]  # Save the extra data in the buffer.
+        self._read_pos = 0
+        return out[:n] if out else nodata_val
+
+    def peek(self, n=0):
+        """Returns buffered bytes without advancing the position.
+
+        The argument indicates a desired minimal number of bytes; we
+        do at most one raw read to satisfy it.  We never return more
+        than self.buffer_size.
+        """
+        with self._read_lock:
+            return self._peek_unlocked(n)
+
+    def _peek_unlocked(self, n=0):
+        want = min(n, self.buffer_size)
+        have = len(self._read_buf) - self._read_pos
+        if have < want or have <= 0:
+            to_read = self.buffer_size - have
+            current = self.raw.read(to_read)
+            if current:
+                self._read_buf = self._read_buf[self._read_pos:] + current
+                self._read_pos = 0
+        return self._read_buf[self._read_pos:]
+
+    def read1(self, n):
+        """Reads up to n bytes, with at most one read() system call."""
+        # Returns up to n bytes.  If at least one byte is buffered, we
+        # only return buffered bytes.  Otherwise, we do one raw read.
+        if n < 0:
+            raise ValueError("number of bytes to read must be positive")
+        if n == 0:
+            return b""
+        with self._read_lock:
+            self._peek_unlocked(1)
+            return self._read_unlocked(
+                min(n, len(self._read_buf) - self._read_pos))
+
+    def tell(self):
+        return _BufferedIOMixin.tell(self) - len(self._read_buf) + self._read_pos
+
+    def seek(self, pos, whence=0):
+        if not (0 <= whence <= 2):
+            raise ValueError("invalid whence value")
+        with self._read_lock:
+            if whence == 1:
+                pos -= len(self._read_buf) - self._read_pos
+            pos = _BufferedIOMixin.seek(self, pos, whence)
+            self._reset_read_buf()
+            return pos
+
+class BufferedWriter(_BufferedIOMixin):
+
+    """A buffer for a writeable sequential RawIO object.
+
+    The constructor creates a BufferedWriter for the given writeable raw
+    stream. If the buffer_size is not given, it defaults to
+    DEFAULT_BUFFER_SIZE.
+    """
+
+    _warning_stack_offset = 2
+
+    def __init__(self, raw,
+                 buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None):
+        if not raw.writable():
+            raise IOError('"raw" argument must be writable.')
+
+        _BufferedIOMixin.__init__(self, raw)
+        if buffer_size <= 0:
+            raise ValueError("invalid buffer size")
+        if max_buffer_size is not None:
+            warnings.warn("max_buffer_size is deprecated", DeprecationWarning,
+                          self._warning_stack_offset)
+        self.buffer_size = buffer_size
+        self._write_buf = bytearray()
+        self._write_lock = Lock()
+
+    def write(self, b):
+        if self.closed:
+            raise ValueError("write to closed file")
+        if isinstance(b, unicode):
+            raise TypeError("can't write unicode to binary stream")
+        with self._write_lock:
+            # XXX we can implement some more tricks to try and avoid
+            # partial writes
+            if len(self._write_buf) > self.buffer_size:
+                # We're full, so let's pre-flush the buffer
+                try:
+                    self._flush_unlocked()
+                except BlockingIOError as e:
+                    # We can't accept anything else.
+                    # XXX Why not just let the exception pass through?
+                    raise BlockingIOError(e.errno, e.strerror, 0)
+            before = len(self._write_buf)
+            self._write_buf.extend(b)
+            written = len(self._write_buf) - before
+            if len(self._write_buf) > self.buffer_size:
+                try:
+                    self._flush_unlocked()
+                except BlockingIOError as e:
+                    if len(self._write_buf) > self.buffer_size:
+                        # We've hit the buffer_size. We have to accept a partial
+                        # write and cut back our buffer.
+                        overage = len(self._write_buf) - self.buffer_size
+                        written -= overage
+                        self._write_buf = self._write_buf[:self.buffer_size]
+                        raise BlockingIOError(e.errno, e.strerror, written)
+            return written
+
+    def truncate(self, pos=None):
+        with self._write_lock:
+            self._flush_unlocked()
+            if pos is None:
+                pos = self.raw.tell()
+            return self.raw.truncate(pos)
+
+    def flush(self):
+        with self._write_lock:
+            self._flush_unlocked()
+
+    def _flush_unlocked(self):
+        if self.closed:
+            raise ValueError("flush of closed file")
+        written = 0
+        try:
+            while self._write_buf:
+                n = self.raw.write(self._write_buf)
+                if n > len(self._write_buf) or n < 0:
+                    raise IOError("write() returned incorrect number of bytes")
+                del self._write_buf[:n]
+                written += n
+        except BlockingIOError as e:
+            n = e.characters_written
+            del self._write_buf[:n]
+            written += n
+            raise BlockingIOError(e.errno, e.strerror, written)
+
+    def tell(self):
+        return _BufferedIOMixin.tell(self) + len(self._write_buf)
+
+    def seek(self, pos, whence=0):
+        if not (0 <= whence <= 2):
+            raise ValueError("invalid whence")
+        with self._write_lock:
+            self._flush_unlocked()
+            return _BufferedIOMixin.seek(self, pos, whence)
+
+
+class BufferedRWPair(BufferedIOBase):
+
+    """A buffered reader and writer object together.
+
+    A buffered reader object and buffered writer object put together to
+    form a sequential IO object that can read and write. This is typically
+    used with a socket or two-way pipe.
+
+    reader and writer are RawIOBase objects that are readable and
+    writeable respectively. If the buffer_size is omitted it defaults to
+    DEFAULT_BUFFER_SIZE.
+    """
+
+    # XXX The usefulness of this (compared to having two separate IO
+    # objects) is questionable.
+
+    def __init__(self, reader, writer,
+                 buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None):
+        """Constructor.
+
+        The arguments are two RawIO instances.
+        """
+        if max_buffer_size is not None:
+            warnings.warn("max_buffer_size is deprecated", DeprecationWarning, 2)
+
+        if not reader.readable():
+            raise IOError('"reader" argument must be readable.')
+
+        if not writer.writable():
+            raise IOError('"writer" argument must be writable.')
+
+        self.reader = BufferedReader(reader, buffer_size)
+        self.writer = BufferedWriter(writer, buffer_size)
+
+    def read(self, n=None):
+        if n is None:
+            n = -1
+        return self.reader.read(n)
+
+    def readinto(self, b):
+        return self.reader.readinto(b)
+
+    def write(self, b):
+        return self.writer.write(b)
+
+    def peek(self, n=0):
+        return self.reader.peek(n)
+
+    def read1(self, n):
+        return self.reader.read1(n)
+
+    def readable(self):
+        return self.reader.readable()
+
+    def writable(self):
+        return self.writer.writable()
+
+    def flush(self):
+        return self.writer.flush()
+
+    def close(self):
+        self.writer.close()
+        self.reader.close()
+
+    def isatty(self):
+        return self.reader.isatty() or self.writer.isatty()
+
+    @property
+    def closed(self):
+        return self.writer.closed
+
+
+class BufferedRandom(BufferedWriter, BufferedReader):
+
+    """A buffered interface to random access streams.
+
+    The constructor creates a reader and writer for a seekable stream,
+    raw, given in the first argument. If the buffer_size is omitted it
+    defaults to DEFAULT_BUFFER_SIZE.
+    """
+
+    _warning_stack_offset = 3
+
+    def __init__(self, raw,
+                 buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None):
+        raw._checkSeekable()
+        BufferedReader.__init__(self, raw, buffer_size)
+        BufferedWriter.__init__(self, raw, buffer_size, max_buffer_size)
+
+    def seek(self, pos, whence=0):
+        if not (0 <= whence <= 2):
+            raise ValueError("invalid whence")
+        self.flush()
+        if self._read_buf:
+            # Undo read ahead.
+            with self._read_lock:
+                self.raw.seek(self._read_pos - len(self._read_buf), 1)
+        # First do the raw seek, then empty the read buffer, so that
+        # if the raw seek fails, we don't lose buffered data forever.
+        pos = self.raw.seek(pos, whence)
+        with self._read_lock:
+            self._reset_read_buf()
+        if pos < 0:
+            raise IOError("seek() returned invalid position")
+        return pos
+
+    def tell(self):
+        if self._write_buf:
+            return BufferedWriter.tell(self)
+        else:
+            return BufferedReader.tell(self)
+
+    def truncate(self, pos=None):
+        if pos is None:
+            pos = self.tell()
+        # Use seek to flush the read buffer.
+        self.seek(pos)
+        return BufferedWriter.truncate(self)
+
+    def read(self, n=None):
+        if n is None:
+            n = -1
+        self.flush()
+        return BufferedReader.read(self, n)
+
+    def readinto(self, b):
+        self.flush()
+        return BufferedReader.readinto(self, b)
+
+    def peek(self, n=0):
+        self.flush()
+        return BufferedReader.peek(self, n)
+
+    def read1(self, n):
+        self.flush()
+        return BufferedReader.read1(self, n)
+
+    def write(self, b):
+        if self._read_buf:
+            # Undo readahead
+            with self._read_lock:
+                self.raw.seek(self._read_pos - len(self._read_buf), 1)
+                self._reset_read_buf()
+        return BufferedWriter.write(self, b)
+
+
+class TextIOBase(IOBase):
+
+    """Base class for text I/O.
+
+    This class provides a character and line based interface to stream
+    I/O. There is no readinto method because Python's character strings
+    are immutable. There is no public constructor.
+    """
+
+    def read(self, n=-1):
+        """Read at most n characters from stream.
+
+        Read from underlying buffer until we have n characters or we hit EOF.
+        If n is negative or omitted, read until EOF.
+        """
+        self._unsupported("read")
+
+    def write(self, s):
+        """Write string s to stream."""
+        self._unsupported("write")
+
+    def truncate(self, pos=None):
+        """Truncate size to pos."""
+        self._unsupported("truncate")
+
+    def readline(self):
+        """Read until newline or EOF.
+
+        Returns an empty string if EOF is hit immediately.
+        """
+        self._unsupported("readline")
+
+    def detach(self):
+        """
+        Separate the underlying buffer from the TextIOBase and return it.
+
+        After the underlying buffer has been detached, the TextIO is in an
+        unusable state.
+        """
+        self._unsupported("detach")
+
+    @property
+    def encoding(self):
+        """Subclasses should override."""
+        return None
+
+    @property
+    def newlines(self):
+        """Line endings translated so far.
+
+        Only line endings translated during reading are considered.
+
+        Subclasses should override.
+        """
+        return None
+
+    @property
+    def errors(self):
+        """Error setting of the decoder or encoder.
+
+        Subclasses should override."""
+        return None
+
+io.TextIOBase.register(TextIOBase)
+
+
+class IncrementalNewlineDecoder(codecs.IncrementalDecoder):
+    r"""Codec used when reading a file in universal newlines mode.  It wraps
+    another incremental decoder, translating \r\n and \r into \n.  It also
+    records the types of newlines encountered.  When used with
+    translate=False, it ensures that the newline sequence is returned in
+    one piece.
+    """
+    def __init__(self, decoder, translate, errors='strict'):
+        codecs.IncrementalDecoder.__init__(self, errors=errors)
+        self.translate = translate
+        self.decoder = decoder
+        self.seennl = 0
+        self.pendingcr = False
+
+    def decode(self, input, final=False):
+        # decode input (with the eventual \r from a previous pass)
+        if self.decoder is None:
+            output = input
+        else:
+            output = self.decoder.decode(input, final=final)
+        if self.pendingcr and (output or final):
+            output = "\r" + output
+            self.pendingcr = False
+
+        # retain last \r even when not translating data:
+        # then readline() is sure to get \r\n in one pass
+        if output.endswith("\r") and not final:
+            output = output[:-1]
+            self.pendingcr = True
+
+        # Record which newlines are read
+        crlf = output.count('\r\n')
+        cr = output.count('\r') - crlf
+        lf = output.count('\n') - crlf
+        self.seennl |= (lf and self._LF) | (cr and self._CR) \
+                    | (crlf and self._CRLF)
+
+        if self.translate:
+            if crlf:
+                output = output.replace("\r\n", "\n")
+            if cr:
+                output = output.replace("\r", "\n")
+
+        return output
+
+    def getstate(self):
+        if self.decoder is None:
+            buf = b""
+            flag = 0
+        else:
+            buf, flag = self.decoder.getstate()
+        flag <<= 1
+        if self.pendingcr:
+            flag |= 1
+        return buf, flag
+
+    def setstate(self, state):
+        buf, flag = state
+        self.pendingcr = bool(flag & 1)
+        if self.decoder is not None:
+            self.decoder.setstate((buf, flag >> 1))
+
+    def reset(self):
+        self.seennl = 0
+        self.pendingcr = False
+        if self.decoder is not None:
+            self.decoder.reset()
+
+    _LF = 1
+    _CR = 2
+    _CRLF = 4
+
+    @property
+    def newlines(self):
+        return (None,
+                "\n",
+                "\r",
+                ("\r", "\n"),
+                "\r\n",
+                ("\n", "\r\n"),
+                ("\r", "\r\n"),
+                ("\r", "\n", "\r\n")
+               )[self.seennl]
+
+
+class TextIOWrapper(TextIOBase):
+
+    r"""Character and line based layer over a BufferedIOBase object, buffer.
+
+    encoding gives the name of the encoding that the stream will be
+    decoded or encoded with. It defaults to locale.getpreferredencoding.
+
+    errors determines the strictness of encoding and decoding (see the
+    codecs.register) and defaults to "strict".
+
+    newline can be None, '', '\n', '\r', or '\r\n'.  It controls the
+    handling of line endings. If it is None, universal newlines is
+    enabled.  With this enabled, on input, the lines endings '\n', '\r',
+    or '\r\n' are translated to '\n' before being returned to the
+    caller. Conversely, on output, '\n' is translated to the system
+    default line seperator, os.linesep. If newline is any other of its
+    legal values, that newline becomes the newline when the file is read
+    and it is returned untranslated. On output, '\n' is converted to the
+    newline.
+
+    If line_buffering is True, a call to flush is implied when a call to
+    write contains a newline character.
+    """
+
+    _CHUNK_SIZE = 2048
+
+    def __init__(self, buffer, encoding=None, errors=None, newline=None,
+                 line_buffering=False):
+        if newline is not None and not isinstance(newline, basestring):
+            raise TypeError("illegal newline type: %r" % (type(newline),))
+        if newline not in (None, "", "\n", "\r", "\r\n"):
+            raise ValueError("illegal newline value: %r" % (newline,))
+        if encoding is None:
+            try:
+                encoding = os.device_encoding(buffer.fileno())
+            except (AttributeError, UnsupportedOperation):
+                pass
+            if encoding is None:
+                try:
+                    import locale
+                except ImportError:
+                    # Importing locale may fail if Python is being built
+                    encoding = "ascii"
+                else:
+                    encoding = locale.getpreferredencoding()
+
+        if not isinstance(encoding, basestring):
+            raise ValueError("invalid encoding: %r" % encoding)
+
+        if errors is None:
+            errors = "strict"
+        else:
+            if not isinstance(errors, basestring):
+                raise ValueError("invalid errors: %r" % errors)
+
+        self.buffer = buffer
+        self._line_buffering = line_buffering
+        self._encoding = encoding
+        self._errors = errors
+        self._readuniversal = not newline
+        self._readtranslate = newline is None
+        self._readnl = newline
+        self._writetranslate = newline != ''
+        self._writenl = newline or os.linesep
+        self._encoder = None
+        self._decoder = None
+        self._decoded_chars = ''  # buffer for text returned from decoder
+        self._decoded_chars_used = 0  # offset into _decoded_chars for read()
+        self._snapshot = None  # info for reconstructing decoder state
+        self._seekable = self._telling = self.buffer.seekable()
+
+        if self._seekable and self.writable():
+            position = self.buffer.tell()
+            if position != 0:
+                try:
+                    self._get_encoder().setstate(0)
+                except LookupError:
+                    # Sometimes the encoder doesn't exist
+                    pass
+
+    # self._snapshot is either None, or a tuple (dec_flags, next_input)
+    # where dec_flags is the second (integer) item of the decoder state
+    # and next_input is the chunk of input bytes that comes next after the
+    # snapshot point.  We use this to reconstruct decoder states in tell().
+
+    # Naming convention:
+    #   - "bytes_..." for integer variables that count input bytes
+    #   - "chars_..." for integer variables that count decoded characters
+
+    def __repr__(self):
+        try:
+            name = self.name
+        except AttributeError:
+            return "<_pyio.TextIOWrapper encoding='{0}'>".format(self.encoding)
+        else:
+            return "<_pyio.TextIOWrapper name={0!r} encoding='{1}'>".format(
+                name, self.encoding)
+
+    @property
+    def encoding(self):
+        return self._encoding
+
+    @property
+    def errors(self):
+        return self._errors
+
+    @property
+    def line_buffering(self):
+        return self._line_buffering
+
+    def seekable(self):
+        return self._seekable
+
+    def readable(self):
+        return self.buffer.readable()
+
+    def writable(self):
+        return self.buffer.writable()
+
+    def flush(self):
+        self.buffer.flush()
+        self._telling = self._seekable
+
+    def close(self):
+        if self.buffer is not None:
+            try:
+                self.flush()
+            except IOError:
+                pass  # If flush() fails, just give up
+            self.buffer.close()
+
+    @property
+    def closed(self):
+        return self.buffer.closed
+
+    @property
+    def name(self):
+        return self.buffer.name
+
+    def fileno(self):
+        return self.buffer.fileno()
+
+    def isatty(self):
+        return self.buffer.isatty()
+
+    def write(self, s):
+        if self.closed:
+            raise ValueError("write to closed file")
+        if not isinstance(s, unicode):
+            raise TypeError("can't write %s to text stream" %
+                            s.__class__.__name__)
+        length = len(s)
+        haslf = (self._writetranslate or self._line_buffering) and "\n" in s
+        if haslf and self._writetranslate and self._writenl != "\n":
+            s = s.replace("\n", self._writenl)
+        encoder = self._encoder or self._get_encoder()
+        # XXX What if we were just reading?
+        b = encoder.encode(s)
+        self.buffer.write(b)
+        if self._line_buffering and (haslf or "\r" in s):
+            self.flush()
+        self._snapshot = None
+        if self._decoder:
+            self._decoder.reset()
+        return length
+
+    def _get_encoder(self):
+        make_encoder = codecs.getincrementalencoder(self._encoding)
+        self._encoder = make_encoder(self._errors)
+        return self._encoder
+
+    def _get_decoder(self):
+        make_decoder = codecs.getincrementaldecoder(self._encoding)
+        decoder = make_decoder(self._errors)
+        if self._readuniversal:
+            decoder = IncrementalNewlineDecoder(decoder, self._readtranslate)
+        self._decoder = decoder
+        return decoder
+
+    # The following three methods implement an ADT for _decoded_chars.
+    # Text returned from the decoder is buffered here until the client
+    # requests it by calling our read() or readline() method.
+    def _set_decoded_chars(self, chars):
+        """Set the _decoded_chars buffer."""
+        self._decoded_chars = chars
+        self._decoded_chars_used = 0
+
+    def _get_decoded_chars(self, n=None):
+        """Advance into the _decoded_chars buffer."""
+        offset = self._decoded_chars_used
+        if n is None:
+            chars = self._decoded_chars[offset:]
+        else:
+            chars = self._decoded_chars[offset:offset + n]
+        self._decoded_chars_used += len(chars)
+        return chars
+
+    def _rewind_decoded_chars(self, n):
+        """Rewind the _decoded_chars buffer."""
+        if self._decoded_chars_used < n:
+            raise AssertionError("rewind decoded_chars out of bounds")
+        self._decoded_chars_used -= n
+
+    def _read_chunk(self):
+        """
+        Read and decode the next chunk of data from the BufferedReader.
+        """
+
+        # The return value is True unless EOF was reached.  The decoded
+        # string is placed in self._decoded_chars (replacing its previous
+        # value).  The entire input chunk is sent to the decoder, though
+        # some of it may remain buffered in the decoder, yet to be
+        # converted.
+
+        if self._decoder is None:
+            raise ValueError("no decoder")
+
+        if self._telling:
+            # To prepare for tell(), we need to snapshot a point in the
+            # file where the decoder's input buffer is empty.
+
+            dec_buffer, dec_flags = self._decoder.getstate()
+            # Given this, we know there was a valid snapshot point
+            # len(dec_buffer) bytes ago with decoder state (b'', dec_flags).
+
+        # Read a chunk, decode it, and put the result in self._decoded_chars.
+        input_chunk = self.buffer.read1(self._CHUNK_SIZE)
+        eof = not input_chunk
+        self._set_decoded_chars(self._decoder.decode(input_chunk, eof))
+
+        if self._telling:
+            # At the snapshot point, len(dec_buffer) bytes before the read,
+            # the next input to be decoded is dec_buffer + input_chunk.
+            self._snapshot = (dec_flags, dec_buffer + input_chunk)
+
+        return not eof
+
+    def _pack_cookie(self, position, dec_flags=0,
+                           bytes_to_feed=0, need_eof=0, chars_to_skip=0):
+        # The meaning of a tell() cookie is: seek to position, set the
+        # decoder flags to dec_flags, read bytes_to_feed bytes, feed them
+        # into the decoder with need_eof as the EOF flag, then skip
+        # chars_to_skip characters of the decoded result.  For most simple
+        # decoders, tell() will often just give a byte offset in the file.
+        return (position | (dec_flags<<64) | (bytes_to_feed<<128) |
+               (chars_to_skip<<192) | bool(need_eof)<<256)
+
+    def _unpack_cookie(self, bigint):
+        rest, position = divmod(bigint, 1<<64)
+        rest, dec_flags = divmod(rest, 1<<64)
+        rest, bytes_to_feed = divmod(rest, 1<<64)
+        need_eof, chars_to_skip = divmod(rest, 1<<64)
+        return position, dec_flags, bytes_to_feed, need_eof, chars_to_skip
+
+    def tell(self):
+        if not self._seekable:
+            raise IOError("underlying stream is not seekable")
+        if not self._telling:
+            raise IOError("telling position disabled by next() call")
+        self.flush()
+        position = self.buffer.tell()
+        decoder = self._decoder
+        if decoder is None or self._snapshot is None:
+            if self._decoded_chars:
+                # This should never happen.
+                raise AssertionError("pending decoded text")
+            return position
+
+        # Skip backward to the snapshot point (see _read_chunk).
+        dec_flags, next_input = self._snapshot
+        position -= len(next_input)
+
+        # How many decoded characters have been used up since the snapshot?
+        chars_to_skip = self._decoded_chars_used
+        if chars_to_skip == 0:
+            # We haven't moved from the snapshot point.
+            return self._pack_cookie(position, dec_flags)
+
+        # Starting from the snapshot position, we will walk the decoder
+        # forward until it gives us enough decoded characters.
+        saved_state = decoder.getstate()
+        try:
+            # Note our initial start point.
+            decoder.setstate((b'', dec_flags))
+            start_pos = position
+            start_flags, bytes_fed, chars_decoded = dec_flags, 0, 0
+            need_eof = 0
+
+            # Feed the decoder one byte at a time.  As we go, note the
+            # nearest "safe start point" before the current location
+            # (a point where the decoder has nothing buffered, so seek()
+            # can safely start from there and advance to this location).
+            for next_byte in next_input:
+                bytes_fed += 1
+                chars_decoded += len(decoder.decode(next_byte))
+                dec_buffer, dec_flags = decoder.getstate()
+                if not dec_buffer and chars_decoded <= chars_to_skip:
+                    # Decoder buffer is empty, so this is a safe start point.
+                    start_pos += bytes_fed
+                    chars_to_skip -= chars_decoded
+                    start_flags, bytes_fed, chars_decoded = dec_flags, 0, 0
+                if chars_decoded >= chars_to_skip:
+                    break
+            else:
+                # We didn't get enough decoded data; signal EOF to get more.
+                chars_decoded += len(decoder.decode(b'', final=True))
+                need_eof = 1
+                if chars_decoded < chars_to_skip:
+                    raise IOError("can't reconstruct logical file position")
+
+            # The returned cookie corresponds to the last safe start point.
+            return self._pack_cookie(
+                start_pos, start_flags, bytes_fed, need_eof, chars_to_skip)
+        finally:
+            decoder.setstate(saved_state)
+
+    def truncate(self, pos=None):
+        self.flush()
+        if pos is None:
+            pos = self.tell()
+        self.seek(pos)
+        return self.buffer.truncate()
+
+    def detach(self):
+        if self.buffer is None:
+            raise ValueError("buffer is already detached")
+        self.flush()
+        buffer = self.buffer
+        self.buffer = None
+        return buffer
+
+    def seek(self, cookie, whence=0):
+        if self.closed:
+            raise ValueError("tell on closed file")
+        if not self._seekable:
+            raise IOError("underlying stream is not seekable")
+        if whence == 1: # seek relative to current position
+            if cookie != 0:
+                raise IOError("can't do nonzero cur-relative seeks")
+            # Seeking to the current position should attempt to
+            # sync the underlying buffer with the current position.
+            whence = 0
+            cookie = self.tell()
+        if whence == 2: # seek relative to end of file
+            if cookie != 0:
+                raise IOError("can't do nonzero end-relative seeks")
+            self.flush()
+            position = self.buffer.seek(0, 2)
+            self._set_decoded_chars('')
+            self._snapshot = None
+            if self._decoder:
+                self._decoder.reset()
+            return position
+        if whence != 0:
+            raise ValueError("invalid whence (%r, should be 0, 1 or 2)" %
+                             (whence,))
+        if cookie < 0:
+            raise ValueError("negative seek position %r" % (cookie,))
+        self.flush()
+
+        # The strategy of seek() is to go back to the safe start point
+        # and replay the effect of read(chars_to_skip) from there.
+        start_pos, dec_flags, bytes_to_feed, need_eof, chars_to_skip = \
+            self._unpack_cookie(cookie)
+
+        # Seek back to the safe start point.
+        self.buffer.seek(start_pos)
+        self._set_decoded_chars('')
+        self._snapshot = None
+
+        # Restore the decoder to its state from the safe start point.
+        if cookie == 0 and self._decoder:
+            self._decoder.reset()
+        elif self._decoder or dec_flags or chars_to_skip:
+            self._decoder = self._decoder or self._get_decoder()
+            self._decoder.setstate((b'', dec_flags))
+            self._snapshot = (dec_flags, b'')
+
+        if chars_to_skip:
+            # Just like _read_chunk, feed the decoder and save a snapshot.
+            input_chunk = self.buffer.read(bytes_to_feed)
+            self._set_decoded_chars(
+                self._decoder.decode(input_chunk, need_eof))
+            self._snapshot = (dec_flags, input_chunk)
+
+            # Skip chars_to_skip of the decoded characters.
+            if len(self._decoded_chars) < chars_to_skip:
+                raise IOError("can't restore logical file position")
+            self._decoded_chars_used = chars_to_skip
+
+        # Finally, reset the encoder (merely useful for proper BOM handling)
+        try:
+            encoder = self._encoder or self._get_encoder()
+        except LookupError:
+            # Sometimes the encoder doesn't exist
+            pass
+        else:
+            if cookie != 0:
+                encoder.setstate(0)
+            else:
+                encoder.reset()
+        return cookie
+
+    def read(self, n=None):
+        self._checkReadable()
+        if n is None:
+            n = -1
+        decoder = self._decoder or self._get_decoder()
+        if n < 0:
+            # Read everything.
+            result = (self._get_decoded_chars() +
+                      decoder.decode(self.buffer.read(), final=True))
+            self._set_decoded_chars('')
+            self._snapshot = None
+            return result
+        else:
+            # Keep reading chunks until we have n characters to return.
+            eof = False
+            result = self._get_decoded_chars(n)
+            while len(result) < n and not eof:
+                eof = not self._read_chunk()
+                result += self._get_decoded_chars(n - len(result))
+            return result
+
+    def next(self):
+        self._telling = False
+        line = self.readline()
+        if not line:
+            self._snapshot = None
+            self._telling = self._seekable
+            raise StopIteration
+        return line
+
+    def readline(self, limit=None):
+        if self.closed:
+            raise ValueError("read from closed file")
+        if limit is None:
+            limit = -1
+        elif not isinstance(limit, (int, long)):
+            raise TypeError("limit must be an integer")
+
+        # Grab all the decoded text (we will rewind any extra bits later).
+        line = self._get_decoded_chars()
+
+        start = 0
+        # Make the decoder if it doesn't already exist.
+        if not self._decoder:
+            self._get_decoder()
+
+        pos = endpos = None
+        while True:
+            if self._readtranslate:
+                # Newlines are already translated, only search for \n
+                pos = line.find('\n', start)
+                if pos >= 0:
+                    endpos = pos + 1
+                    break
+                else:
+                    start = len(line)
+
+            elif self._readuniversal:
+                # Universal newline search. Find any of \r, \r\n, \n
+                # The decoder ensures that \r\n are not split in two pieces
+
+                # In C we'd look for these in parallel of course.
+                nlpos = line.find("\n", start)
+                crpos = line.find("\r", start)
+                if crpos == -1:
+                    if nlpos == -1:
+                        # Nothing found
+                        start = len(line)
+                    else:
+                        # Found \n
+                        endpos = nlpos + 1
+                        break
+                elif nlpos == -1:
+                    # Found lone \r
+                    endpos = crpos + 1
+                    break
+                elif nlpos < crpos:
+                    # Found \n
+                    endpos = nlpos + 1
+                    break
+                elif nlpos == crpos + 1:
+                    # Found \r\n
+                    endpos = crpos + 2
+                    break
+                else:
+                    # Found \r
+                    endpos = crpos + 1
+                    break
+            else:
+                # non-universal
+                pos = line.find(self._readnl)
+                if pos >= 0:
+                    endpos = pos + len(self._readnl)
+                    break
+
+            if limit >= 0 and len(line) >= limit:
+                endpos = limit  # reached length limit
+                break
+
+            # No line ending seen yet - get more data'
+            while self._read_chunk():
+                if self._decoded_chars:
+                    break
+            if self._decoded_chars:
+                line += self._get_decoded_chars()
+            else:
+                # end of file
+                self._set_decoded_chars('')
+                self._snapshot = None
+                return line
+
+        if limit >= 0 and endpos > limit:
+            endpos = limit  # don't exceed limit
+
+        # Rewind _decoded_chars to just after the line ending we found.
+        self._rewind_decoded_chars(len(line) - endpos)
+        return line[:endpos]
+
+    @property
+    def newlines(self):
+        return self._decoder.newlines if self._decoder else None
+
+
+class StringIO(TextIOWrapper):
+    """Text I/O implementation using an in-memory buffer.
+
+    The initial_value argument sets the value of object.  The newline
+    argument is like the one of TextIOWrapper's constructor.
+    """
+
+    def __init__(self, initial_value="", newline="\n"):
+        super(StringIO, self).__init__(BytesIO(),
+                                       encoding="utf-8",
+                                       errors="strict",
+                                       newline=newline)
+        # Issue #5645: make universal newlines semantics the same as in the
+        # C version, even under Windows.
+        if newline is None:
+            self._writetranslate = False
+        if initial_value:
+            if not isinstance(initial_value, unicode):
+                initial_value = unicode(initial_value)
+            self.write(initial_value)
+            self.seek(0)
+
+    def getvalue(self):
+        self.flush()
+        return self.buffer.getvalue().decode(self._encoding, self._errors)
+
+    def __repr__(self):
+        # TextIOWrapper tells the encoding in its repr. In StringIO,
+        # that's a implementation detail.
+        return object.__repr__(self)
+
+    @property
+    def errors(self):
+        return None
+
+    @property
+    def encoding(self):
+        return None
+
+    def detach(self):
+        # This doesn't make sense on StringIO.
+        self._unsupported("detach")