Issue 2918: Merge StringIO and cStringIO.

8 files changed, 702 insertions, 22 deletions

diff --git a/Lib/io.py b/Lib/io.py
index 0c993b1..f543e20 100644
--- a/Lib/io.py
+++ b/Lib/io.py
@@ -1769,20 +1769,20 @@ class TextIOWrapper(TextIOBase):
     def newlines(self):
         return self._decoder.newlines if self._decoder else None
 
-class StringIO(TextIOWrapper):
-    """An in-memory stream for text. The initial_value argument sets the
-    value of object. The other arguments are like those of TextIOWrapper's
-    constructor.
+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.
     """
 
     # XXX This is really slow, but fully functional
 
-    def __init__(self, initial_value="", encoding="utf-8",
-                 errors="strict", newline="\n"):
-        super(StringIO, self).__init__(BytesIO(),
-                                       encoding=encoding,
-                                       errors=errors,
-                                       newline=newline)
+    def __init__(self, initial_value="", newline="\n"):
+        super(_StringIO, self).__init__(BytesIO(),
+                                        encoding="utf-8",
+                                        errors="strict",
+                                        newline=newline)
         if initial_value:
             if not isinstance(initial_value, str):
                 initial_value = str(initial_value)
@@ -1792,3 +1792,271 @@ class StringIO(TextIOWrapper):
     def getvalue(self):
         self.flush()
         return self.buffer.getvalue().decode(self._encoding, self._errors)
+
+try:
+    import _stringio
+
+    # This subclass is a reimplementation of the TextIOWrapper
+    # interface without any of its text decoding facilities. All the
+    # stored data is manipulated with the efficient
+    # _stringio._StringIO extension type. Also, the newline decoding
+    # mechanism of IncrementalNewlineDecoder is reimplemented here for
+    # efficiency. Doing otherwise, would require us to implement a
+    # fake decoder which would add an additional and unnecessary layer
+    # on top of the _StringIO methods.
+
+    class StringIO(_stringio._StringIO, TextIOBase):
+        """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.
+        """
+
+        _CHUNK_SIZE = 4096
+
+        def __init__(self, initial_value="", newline="\n"):
+            if newline not in (None, "", "\n", "\r", "\r\n"):
+                raise ValueError("illegal newline value: %r" % (newline,))
+
+            self._readuniversal = not newline
+            self._readtranslate = newline is None
+            self._readnl = newline
+            self._writetranslate = newline != ""
+            self._writenl = newline or os.linesep
+            self._pending = ""
+            self._seennl = 0
+
+            # Reset the buffer first, in case __init__ is called
+            # multiple times.
+            self.truncate(0)
+            if initial_value is None:
+                initial_value = ""
+            self.write(initial_value)
+            self.seek(0)
+
+        @property
+        def buffer(self):
+            raise UnsupportedOperation("%s.buffer attribute is unsupported" %
+                                       self.__class__.__name__)
+
+        def _decode_newlines(self, input, final=False):
+            # decode input (with the eventual \r from a previous pass)
+            if self._pending:
+                input = self._pending + input
+
+            # retain last \r even when not translating data:
+            # then readline() is sure to get \r\n in one pass
+            if input.endswith("\r") and not final:
+                input = input[:-1]
+                self._pending = "\r"
+            else:
+                self._pending = ""
+
+            # Record which newlines are read
+            crlf = input.count('\r\n')
+            cr = input.count('\r') - crlf
+            lf = input.count('\n') - crlf
+            self._seennl |= (lf and self._LF) | (cr and self._CR) \
+                         | (crlf and self._CRLF)
+
+            if self._readtranslate:
+                if crlf:
+                    output = input.replace("\r\n", "\n")
+                if cr:
+                    output = input.replace("\r", "\n")
+            else:
+                output = input
+
+            return output
+
+        def writable(self):
+            return True
+
+        def readable(self):
+            return True
+
+        def seekable(self):
+            return True
+
+        _read = _stringio._StringIO.read
+        _write = _stringio._StringIO.write
+        _tell = _stringio._StringIO.tell
+        _seek = _stringio._StringIO.seek
+        _truncate = _stringio._StringIO.truncate
+        _getvalue = _stringio._StringIO.getvalue
+
+        def getvalue(self) -> str:
+            """Retrieve the entire contents of the object."""
+            if self.closed:
+                raise ValueError("read on closed file")
+            return self._getvalue()
+
+        def write(self, s: str) -> int:
+            """Write string s to file.
+
+            Returns the number of characters written.
+            """
+            if self.closed:
+                raise ValueError("write to closed file")
+            if not isinstance(s, str):
+                raise TypeError("can't write %s to text stream" %
+                                s.__class__.__name__)
+            length = len(s)
+            if self._writetranslate and self._writenl != "\n":
+                s = s.replace("\n", self._writenl)
+            self._pending = ""
+            self._write(s)
+            return length
+
+        def read(self, n: int = None) -> str:
+            """Read at most n characters, returned as a string.
+
+            If the argument is negative or omitted, read until EOF
+            is reached. Return an empty string at EOF.
+            """
+            if self.closed:
+                raise ValueError("read to closed file")
+            if n is None:
+                n = -1
+            res = self._pending
+            if n < 0:
+                res += self._decode_newlines(self._read(), True)
+                self._pending = ""
+                return res
+            else:
+                res = self._decode_newlines(self._read(n), True)
+                self._pending = res[n:]
+                return res[:n]
+
+        def tell(self) -> int:
+            """Tell the current file position."""
+            if self.closed:
+                raise ValueError("tell from closed file")
+            if self._pending:
+                return self._tell() - len(self._pending)
+            else:
+                return self._tell()
+
+        def seek(self, pos: int = None, whence: int = 0) -> int:
+            """Change stream position.
+
+            Seek to character offset pos relative to position indicated by whence:
+                0  Start of stream (the default).  pos should be >= 0;
+                1  Current position - pos must be 0;
+                2  End of stream - pos must be 0.
+            Returns the new absolute position.
+            """
+            if self.closed:
+                raise ValueError("seek from closed file")
+            self._pending = ""
+            return self._seek(pos, whence)
+
+        def truncate(self, pos: int = None) -> int:
+            """Truncate size to pos.
+
+            The pos argument defaults to the current file position, as
+            returned by tell().  Imply an absolute seek to pos.
+            Returns the new absolute position.
+            """
+            if self.closed:
+                raise ValueError("truncate from closed file")
+            self._pending = ""
+            return self._truncate(pos)
+
+        def readline(self, limit: int = None) -> str:
+            if self.closed:
+                raise ValueError("read from closed file")
+            if limit is None:
+                limit = -1
+            if limit >= 0:
+                # XXX: Hack to support limit argument, for backwards
+                # XXX  compatibility
+                line = self.readline()
+                if len(line) <= limit:
+                    return line
+                line, self._pending = line[:limit], line[limit:] + self._pending
+                return line
+
+            line = self._pending
+            self._pending = ""
+
+            start = 0
+            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
+
+                # No line ending seen yet - get more data
+                more_line = self.read(self._CHUNK_SIZE)
+                if more_line:
+                    line += more_line
+                else:
+                    # end of file
+                    return line
+
+            self._pending = line[endpos:]
+            return line[:endpos]
+
+        _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]
+
+
+except ImportError:
+    StringIO = _StringIO
diff --git a/Lib/test/test_memoryio.py b/Lib/test/test_memoryio.py
index 2d91cbd..d1745bc 100644
--- a/Lib/test/test_memoryio.py
+++ b/Lib/test/test_memoryio.py
@@ -10,7 +10,7 @@ import io
 import sys
 
 try:
-    import _bytesio
+    import _bytesio, _stringio
     has_c_implementation = True
 except ImportError:
     has_c_implementation = False
@@ -373,7 +373,7 @@ class PyBytesIOTest(MemoryTestMixin, unittest.TestCase):
 
 class PyStringIOTest(MemoryTestMixin, unittest.TestCase):
     buftype = str
-    ioclass = io.StringIO
+    ioclass = io._StringIO
     EOF = ""
 
     def test_relative_seek(self):
@@ -404,10 +404,14 @@ if has_c_implementation:
     class CBytesIOTest(PyBytesIOTest):
         ioclass = io.BytesIO
 
+    class CStringIOTest(PyStringIOTest):
+        ioclass = io.StringIO
+
+
 def test_main():
     tests = [PyBytesIOTest, PyStringIOTest]
     if has_c_implementation:
-        tests.extend([CBytesIOTest])
+        tests.extend([CBytesIOTest, CStringIOTest])
     support.run_unittest(*tests)
 
 if __name__ == '__main__':
diff --git a/Lib/test/test_minidom.py b/Lib/test/test_minidom.py
index ca1f836..c4c568f 100644
--- a/Lib/test/test_minidom.py
+++ b/Lib/test/test_minidom.py
@@ -3,7 +3,6 @@
 import os
 import sys
 import pickle
-from io import StringIO
 from test.support import verbose, run_unittest, TestSkipped
 import unittest
 
@@ -80,7 +79,7 @@ class MinidomTest(unittest.TestCase):
         self.confirm(t == s, "looking for %s, found %s" % (repr(s), repr(t)))
 
     def testParseFromFile(self):
-        dom = parse(StringIO(open(tstfile).read()))
+        dom = parse(open(tstfile))
         dom.unlink()
         self.confirm(isinstance(dom, Document))
 
diff --git a/Lib/test/test_uu.py b/Lib/test/test_uu.py
index 02d0171..d2b6e73 100644
--- a/Lib/test/test_uu.py
+++ b/Lib/test/test_uu.py
@@ -17,6 +17,32 @@ encodedtext = b"""\
 M5&AE('-M;V]T:\"US8V%L960@<'ET:&]N(&-R97!T(&]V97(@=&AE('-L965P
 (:6YG(&1O9PH """
 
+# Stolen from io.py
+class FakeIO(io.TextIOWrapper):
+    """Text I/O implementation using an in-memory buffer.
+
+    Can be a used as a drop-in replacement for sys.stdin and sys.stdout.
+    """
+
+    # XXX This is really slow, but fully functional
+
+    def __init__(self, initial_value="", encoding="utf-8",
+                 errors="strict", newline="\n"):
+        super(FakeIO, self).__init__(io.BytesIO(),
+                                     encoding=encoding,
+                                     errors=errors,
+                                     newline=newline)
+        if initial_value:
+            if not isinstance(initial_value, str):
+                initial_value = str(initial_value)
+            self.write(initial_value)
+            self.seek(0)
+
+    def getvalue(self):
+        self.flush()
+        return self.buffer.getvalue().decode(self._encoding, self._errors)
+
+
 def encodedtextwrapped(mode, filename):
     return (bytes("begin %03o %s\n" % (mode, filename), "ascii") +
             encodedtext + b"\n \nend\n")
@@ -76,15 +102,15 @@ class UUStdIOTest(unittest.TestCase):
         sys.stdout = self.stdout
 
     def test_encode(self):
-        sys.stdin = io.StringIO(plaintext.decode("ascii"))
-        sys.stdout = io.StringIO()
+        sys.stdin = FakeIO(plaintext.decode("ascii"))
+        sys.stdout = FakeIO()
         uu.encode("-", "-", "t1", 0o666)
         self.assertEqual(sys.stdout.getvalue(),
                          encodedtextwrapped(0o666, "t1").decode("ascii"))
 
     def test_decode(self):
-        sys.stdin = io.StringIO(encodedtextwrapped(0o666, "t1").decode("ascii"))
-        sys.stdout = io.StringIO()
+        sys.stdin = FakeIO(encodedtextwrapped(0o666, "t1").decode("ascii"))
+        sys.stdout = FakeIO()
         uu.decode("-", "-")
         stdout = sys.stdout
         sys.stdout = self.stdout
diff --git a/Lib/xml/dom/minidom.py b/Lib/xml/dom/minidom.py
index f229369..3025ed7 100644
--- a/Lib/xml/dom/minidom.py
+++ b/Lib/xml/dom/minidom.py
@@ -14,6 +14,7 @@ Todo:
  * SAX 2 namespaces
 """
 
+import codecs
 import io
 import xml.dom
 
@@ -49,16 +50,16 @@ class Node(xml.dom.Node):
         # indent = the indentation string to prepend, per level
         # newl = the newline string to append
         use_encoding = "utf-8" if encoding is None else encoding
-        writer = io.StringIO(encoding=use_encoding)
+        writer = codecs.getwriter(use_encoding)(io.BytesIO())
         if self.nodeType == Node.DOCUMENT_NODE:
             # Can pass encoding only to document, to put it into XML header
             self.writexml(writer, "", indent, newl, encoding)
         else:
             self.writexml(writer, "", indent, newl)
         if encoding is None:
-            return writer.getvalue()
+            return writer.stream.getvalue().decode(use_encoding)
         else:
-            return writer.buffer.getvalue()
+            return writer.stream.getvalue()
 
     def hasChildNodes(self):
         if self.childNodes:
diff --git a/Misc/NEWS b/Misc/NEWS
index 6bf1441..c6f91ef 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -78,6 +78,8 @@ Extension Modules
 Library
 -------
 
+- Added C optimized implementation of io.StringIO.
+
 - The ``pickle`` module is now automatically use an optimized C
   implementation of Pickler and Unpickler when available. The
   ``cPickle`` module is no longer needed.
diff --git a/Modules/_stringio.c b/Modules/_stringio.c
new file mode 100644
index 0000000..83fc79e
--- /dev/null
+++ b/Modules/_stringio.c
@@ -0,0 +1,379 @@
+#include "Python.h"
+
+/* This module is a stripped down version of _bytesio.c with a Py_UNICODE
+   buffer. Most of the functionality is provided by subclassing _StringIO. */
+
+
+typedef struct {
+    PyObject_HEAD
+    Py_UNICODE *buf;
+    Py_ssize_t pos;
+    Py_ssize_t string_size;
+    size_t buf_size;
+} StringIOObject;
+
+
+/* Internal routine for changing the size, in terms of characters, of the
+   buffer of StringIO objects.  The caller should ensure that the 'size'
+   argument is non-negative.  Returns 0 on success, -1 otherwise. */
+static int
+resize_buffer(StringIOObject *self, size_t size)
+{
+    /* Here, unsigned types are used to avoid dealing with signed integer
+       overflow, which is undefined in C. */
+    size_t alloc = self->buf_size;
+    Py_UNICODE *new_buf = NULL;
+
+    assert(self->buf != NULL);
+
+    /* For simplicity, stay in the range of the signed type. Anyway, Python
+       doesn't allow strings to be longer than this. */
+    if (size > PY_SSIZE_T_MAX)
+        goto overflow;
+
+    if (size < alloc / 2) {
+        /* Major downsize; resize down to exact size. */
+        alloc = size + 1;
+    }
+    else if (size < alloc) {
+        /* Within allocated size; quick exit */
+        return 0;
+    }
+    else if (size <= alloc * 1.125) {
+        /* Moderate upsize; overallocate similar to list_resize() */
+        alloc = size + (size >> 3) + (size < 9 ? 3 : 6);
+    }
+    else {
+        /* Major upsize; resize up to exact size */
+        alloc = size + 1;
+    }
+
+    if (alloc > ((size_t)-1) / sizeof(Py_UNICODE))
+        goto overflow;
+    new_buf = (Py_UNICODE *)PyMem_Realloc(self->buf,
+                                          alloc * sizeof(Py_UNICODE));
+    if (new_buf == NULL) {
+        PyErr_NoMemory();
+        return -1;
+    }
+    self->buf_size = alloc;
+    self->buf = new_buf;
+
+    return 0;
+
+  overflow:
+    PyErr_SetString(PyExc_OverflowError,
+                    "new buffer size too large");
+    return -1;
+}
+
+/* Internal routine for writing a string of characters to the buffer of a
+   StringIO object. Returns the number of bytes wrote, or -1 on error. */
+static Py_ssize_t
+write_str(StringIOObject *self, const Py_UNICODE *str, Py_ssize_t len)
+{
+    assert(self->buf != NULL);
+    assert(self->pos >= 0);
+    assert(len >= 0);
+
+    /* This overflow check is not strictly necessary. However, it avoids us to
+       deal with funky things like comparing an unsigned and a signed
+       integer. */
+    if (self->pos > PY_SSIZE_T_MAX - len) {
+        PyErr_SetString(PyExc_OverflowError,
+                        "new position too large");
+        return -1;
+    }
+    if (self->pos + len > self->string_size) {
+        if (resize_buffer(self, self->pos + len) < 0)
+            return -1;
+    }
+
+    if (self->pos > self->string_size) {
+        /* In case of overseek, pad with null bytes the buffer region between
+           the end of stream and the current position.
+
+          0   lo      string_size                           hi
+          |   |<---used--->|<----------available----------->|
+          |   |            <--to pad-->|<---to write--->    |
+          0   buf                   positon
+
+        */
+        memset(self->buf + self->string_size, '\0',
+               (self->pos - self->string_size) * sizeof(Py_UNICODE));
+    }
+
+    /* Copy the data to the internal buffer, overwriting some of the
+       existing data if self->pos < self->string_size. */
+    memcpy(self->buf + self->pos, str, len * sizeof(Py_UNICODE));
+    self->pos += len;
+
+    /* Set the new length of the internal string if it has changed */
+    if (self->string_size < self->pos) {
+        self->string_size = self->pos;
+    }
+
+    return len;
+}
+
+static PyObject *
+stringio_getvalue(StringIOObject *self)
+{
+    return PyUnicode_FromUnicode(self->buf, self->string_size);
+}
+
+static PyObject *
+stringio_tell(StringIOObject *self)
+{
+    return PyLong_FromSsize_t(self->pos);
+}
+
+static PyObject *
+stringio_read(StringIOObject *self, PyObject *args)
+{
+    Py_ssize_t size, n;
+    Py_UNICODE *output;
+    PyObject *arg = Py_None;
+
+    if (!PyArg_ParseTuple(args, "|O:read", &arg))
+        return NULL;
+
+    if (PyLong_Check(arg)) {
+        size = PyLong_AsSsize_t(arg);
+    }
+    else if (arg == Py_None) {
+        /* Read until EOF is reached, by default. */
+        size = -1;
+    }
+    else {
+        PyErr_Format(PyExc_TypeError, "integer argument expected, got '%s'",
+                     Py_TYPE(arg)->tp_name);
+        return NULL;
+    }
+
+    /* adjust invalid sizes */
+    n = self->string_size - self->pos;
+    if (size < 0 || size > n) {
+        size = n;
+        if (size < 0)
+            size = 0;
+    }
+
+    assert(self->buf != NULL);
+    output = self->buf + self->pos;
+    self->pos += size;
+
+    return PyUnicode_FromUnicode(output, size);
+}
+
+static PyObject *
+stringio_truncate(StringIOObject *self, PyObject *args)
+{
+    Py_ssize_t size;
+    PyObject *arg = Py_None;
+
+    if (!PyArg_ParseTuple(args, "|O:truncate", &arg))
+        return NULL;
+
+    if (PyLong_Check(arg)) {
+        size = PyLong_AsSsize_t(arg);
+    }
+    else if (arg == Py_None) {
+        /* Truncate to current position if no argument is passed. */
+        size = self->pos;
+    }
+    else {
+        PyErr_Format(PyExc_TypeError, "integer argument expected, got '%s'",
+                     Py_TYPE(arg)->tp_name);
+        return NULL;
+    }
+
+    if (size < 0) {
+        PyErr_Format(PyExc_ValueError,
+                     "Negative size value %zd", size);
+        return NULL;
+    }
+
+    if (size < self->string_size) {
+        self->string_size = size;
+        if (resize_buffer(self, size) < 0)
+            return NULL;
+    }
+    self->pos = size;
+
+    return PyLong_FromSsize_t(size);
+}
+
+static PyObject *
+stringio_seek(StringIOObject *self, PyObject *args)
+{
+    Py_ssize_t pos;
+    int mode = 0;
+
+    if (!PyArg_ParseTuple(args, "n|i:seek", &pos, &mode))
+        return NULL;
+
+    if (mode != 0 && mode != 1 && mode != 2) {
+        PyErr_Format(PyExc_ValueError,
+                     "Invalid whence (%i, should be 0, 1 or 2)", mode);
+        return NULL;
+    }
+    else if (pos < 0 && mode == 0) {
+        PyErr_Format(PyExc_ValueError,
+                     "Negative seek position %zd", pos);
+        return NULL;
+    }
+    else if (mode != 0 && pos != 0) {
+        PyErr_SetString(PyExc_IOError,
+                        "Can't do nonzero cur-relative seeks");
+        return NULL;
+    }
+
+    /* mode 0: offset relative to beginning of the string.
+       mode 1: no change to current position.
+       mode 2: change position to end of file. */
+    if (mode == 1) {
+        pos = self->pos;
+    }
+    else if (mode == 2) {
+        pos = self->string_size;
+    }
+
+    self->pos = pos;
+
+    return PyLong_FromSsize_t(self->pos);
+}
+
+static PyObject *
+stringio_write(StringIOObject *self, PyObject *obj)
+{
+    const Py_UNICODE *str;
+    Py_ssize_t size;
+    Py_ssize_t n = 0;
+
+    if (PyUnicode_Check(obj)) {
+        str = PyUnicode_AsUnicode(obj);
+        size = PyUnicode_GetSize(obj);
+    }
+    else {
+        PyErr_Format(PyExc_TypeError, "string argument expected, got '%s'",
+                     Py_TYPE(obj)->tp_name);
+        return NULL;
+    }
+
+    if (size != 0) {
+        n = write_str(self, str, size);
+        if (n < 0)
+            return NULL;
+    }
+
+    return PyLong_FromSsize_t(n);
+}
+
+static void
+stringio_dealloc(StringIOObject *self)
+{
+    PyMem_Free(self->buf);
+    Py_TYPE(self)->tp_free(self);
+}
+
+static PyObject *
+stringio_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
+{
+    StringIOObject *self;
+
+    assert(type != NULL && type->tp_alloc != NULL);
+    self = (StringIOObject *)type->tp_alloc(type, 0);
+    if (self == NULL)
+        return NULL;
+
+    self->string_size = 0;
+    self->pos = 0;
+    self->buf_size = 0;
+    self->buf = (Py_UNICODE *)PyMem_Malloc(0);
+    if (self->buf == NULL) {
+        Py_DECREF(self);
+        return PyErr_NoMemory();
+    }
+
+    return (PyObject *)self;
+}
+
+static struct PyMethodDef stringio_methods[] = {
+    {"getvalue",   (PyCFunction)stringio_getvalue, METH_VARARGS, NULL},
+    {"read",       (PyCFunction)stringio_read,     METH_VARARGS, NULL},
+    {"tell",       (PyCFunction)stringio_tell,     METH_NOARGS,  NULL},
+    {"truncate",   (PyCFunction)stringio_truncate, METH_VARARGS, NULL},
+    {"seek",       (PyCFunction)stringio_seek,     METH_VARARGS, NULL},
+    {"write",      (PyCFunction)stringio_write,    METH_O,       NULL},
+    {NULL, NULL}        /* sentinel */
+};
+
+static PyTypeObject StringIO_Type = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    "_stringio._StringIO",                     /*tp_name*/
+    sizeof(StringIOObject),                    /*tp_basicsize*/
+    0,                                         /*tp_itemsize*/
+    (destructor)stringio_dealloc,              /*tp_dealloc*/
+    0,                                         /*tp_print*/
+    0,                                         /*tp_getattr*/
+    0,                                         /*tp_setattr*/
+    0,                                         /*tp_compare*/
+    0,                                         /*tp_repr*/
+    0,                                         /*tp_as_number*/
+    0,                                         /*tp_as_sequence*/
+    0,                                         /*tp_as_mapping*/
+    0,                                         /*tp_hash*/
+    0,                                         /*tp_call*/
+    0,                                         /*tp_str*/
+    0,                                         /*tp_getattro*/
+    0,                                         /*tp_setattro*/
+    0,                                         /*tp_as_buffer*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  /*tp_flags*/
+    0,                                         /*tp_doc*/
+    0,                                         /*tp_traverse*/
+    0,                                         /*tp_clear*/
+    0,                                         /*tp_richcompare*/
+    0,                                         /*tp_weaklistoffset*/
+    0,                                         /*tp_iter*/
+    0,                                         /*tp_iternext*/
+    stringio_methods,                          /*tp_methods*/
+    0,                                         /*tp_members*/
+    0,                                         /*tp_getset*/
+    0,                                         /*tp_base*/
+    0,                                         /*tp_dict*/
+    0,                                         /*tp_descr_get*/
+    0,                                         /*tp_descr_set*/
+    0,                                         /*tp_dictoffset*/
+    0,                                         /*tp_init*/
+    0,                                         /*tp_alloc*/
+    stringio_new,                              /*tp_new*/
+};
+
+static struct PyModuleDef _stringiomodule = {
+	PyModuleDef_HEAD_INIT,
+	"_stringio",
+	NULL,
+	-1,
+	NULL,
+	NULL,
+	NULL,
+	NULL,
+	NULL
+};
+
+PyMODINIT_FUNC
+PyInit__stringio(void)
+{
+    PyObject *m;
+
+    if (PyType_Ready(&StringIO_Type) < 0)
+        return NULL;
+    m = PyModule_Create(&_stringiomodule);
+    if (m == NULL)
+        return NULL;
+    Py_INCREF(&StringIO_Type);
+    if (PyModule_AddObject(m, "_StringIO", (PyObject *)&StringIO_Type) < 0)
+        return NULL;
+    return m;
+}
diff --git a/setup.py b/setup.py
index 54868fe..8ca5808 100644
--- a/setup.py
+++ b/setup.py
@@ -422,6 +422,7 @@ class PyBuildExt(build_ext):
         exts.append( Extension("_functools", ["_functoolsmodule.c"]) )
         # Memory-based IO accelerator modules
         exts.append( Extension("_bytesio", ["_bytesio.c"]) )
+        exts.append( Extension("_stringio", ["_stringio.c"]) )
         # C-optimized pickle replacement
         exts.append( Extension("_pickle", ["_pickle.c"]) )
         # atexit