Added fast alternate io.BytesIO implementation and its test suite.

Removed old test suite for StringIO.
Modified truncate() to imply a seek to given argument value.

6 files changed, 481 insertions, 143 deletions

diff --git a/Lib/io.py b/Lib/io.py
index 3172554..3a1546a 100644
--- a/Lib/io.py
+++ b/Lib/io.py
@@ -490,6 +490,7 @@ class IOBase(metaclass=abc.ABCMeta):
         terminator(s) recognized.
         """
         # For backwards compatibility, a (slowish) readline().
+        self._checkClosed()
         if hasattr(self, "peek"):
             def nreadahead():
                 readahead = self.peek(1)
@@ -531,7 +532,7 @@ class IOBase(metaclass=abc.ABCMeta):
         lines will be read if the total size (in bytes/characters) of all
         lines so far exceeds hint.
         """
-        if hint is None:
+        if hint is None or hint <= 0:
             return list(self)
         n = 0
         lines = []
@@ -726,6 +727,8 @@ class _BufferedIOMixin(BufferedIOBase):
 
         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 ###
@@ -765,7 +768,7 @@ class _BufferedIOMixin(BufferedIOBase):
         return self.raw.isatty()
 
 
-class BytesIO(BufferedIOBase):
+class _BytesIO(BufferedIOBase):
 
     """Buffered I/O implementation using an in-memory bytes buffer."""
 
@@ -779,13 +782,19 @@ class BytesIO(BufferedIOBase):
     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 n < 0:
             n = len(self._buffer)
+        if len(self._buffer) <= self._pos:
+            return self._buffer[:0]
         newpos = min(len(self._buffer), self._pos + n)
         b = self._buffer[self._pos : newpos]
         self._pos = newpos
@@ -802,6 +811,8 @@ class BytesIO(BufferedIOBase):
         if isinstance(b, str):
             raise TypeError("can't write str to binary stream")
         n = len(b)
+        if n == 0:
+            return 0
         newpos = self._pos + n
         if newpos > len(self._buffer):
             # Inserts null bytes between the current end of the file
@@ -813,28 +824,38 @@ class BytesIO(BufferedIOBase):
         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") from err
         if whence == 0:
             self._pos = max(0, pos)
+            if pos < 0:
+                raise ValueError("negative seek position %r" % (pos,))
         elif whence == 1:
             self._pos = max(0, self._pos + pos)
         elif whence == 2:
             self._pos = max(0, len(self._buffer) + pos)
         else:
-            raise IOError("invalid whence value")
+            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 pos
+        return self.seek(pos)
 
     def readable(self):
         return True
@@ -845,6 +866,16 @@ class BytesIO(BufferedIOBase):
     def seekable(self):
         return True
 
+# Use the faster implementation of BytesIO if available
+try:
+    import _bytesio
+
+    class BytesIO(_bytesio._BytesIO, BufferedIOBase):
+        __doc__ = _bytesio._BytesIO.__doc__
+
+except ImportError:
+    BytesIO = _BytesIO
+
 
 class BufferedReader(_BufferedIOMixin):
 
@@ -978,6 +1009,12 @@ class BufferedWriter(_BufferedIOMixin):
                     raise BlockingIOError(e.errno, e.strerror, overage)
         return written
 
+    def truncate(self, pos=None):
+        self.flush()
+        if pos is None:
+            pos = self.raw.tell()
+        return self.raw.truncate(pos)
+
     def flush(self):
         if self.closed:
             raise ValueError("flush of closed file")
@@ -1097,6 +1134,13 @@ class BufferedRandom(BufferedWriter, BufferedReader):
         else:
             return self.raw.tell() - len(self._read_buf)
 
+    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
@@ -1145,11 +1189,7 @@ class TextIOBase(IOBase):
 
     def truncate(self, pos: int = None) -> int:
         """Truncate size to pos."""
-        self.flush()
-        if pos is None:
-            pos = self.tell()
-        self.seek(pos)
-        return self.buffer.truncate()
+        self._unsupported("truncate")
 
     def readline(self) -> str:
         """Read until newline or EOF.
@@ -1346,6 +1386,12 @@ class TextIOWrapper(TextIOBase):
     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
@@ -1539,7 +1585,16 @@ class TextIOWrapper(TextIOBase):
         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 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
@@ -1626,6 +1681,8 @@ class TextIOWrapper(TextIOBase):
         return line
 
     def readline(self, limit=None):
+        if self.closed:
+            raise ValueError("read from closed file")
         if limit is None:
             limit = -1
 
diff --git a/Lib/test/test_StringIO.py b/Lib/test/test_StringIO.py
deleted file mode 100644
index 4f3ce83..0000000
--- a/Lib/test/test_StringIO.py
+++ /dev/null
@@ -1,127 +0,0 @@
-# Tests StringIO and cStringIO
-
-import sys
-import unittest
-import io
-from test import test_support
-
-
-class TestGenericStringIO:
-    # use a class variable CLASS to define which class is being tested
-    CLASS = None
-
-    # Line of data to test as string
-    _line = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!'
-
-    # Constructor to use for the test data (._line is passed to this
-    # constructor)
-    constructor = str
-
-    def setUp(self):
-        self._line = self.constructor(self._line)
-        self._lines = self.constructor((self._line + '\n') * 5)
-        self._fp = self.CLASS(self._lines)
-
-    def test_reads(self):
-        eq = self.assertEqual
-        self.assertRaises(TypeError, self._fp.seek)
-        eq(self._fp.read(10), self._line[:10])
-        eq(self._fp.readline(), self._line[10:] + '\n')
-        eq(len(self._fp.readlines(60)), 2)
-
-    def test_writes(self):
-        f = self.CLASS()
-        self.assertRaises(TypeError, f.seek)
-        f.write(self._line[:6])
-        f.seek(3)
-        f.write(self._line[20:26])
-        f.write(self._line[52])
-        self.assertEqual(f.getvalue(), 'abcuvwxyz!')
-
-    def test_writelines(self):
-        f = self.CLASS()
-        f.writelines([self._line[0], self._line[1], self._line[2]])
-        f.seek(0)
-        self.assertEqual(f.getvalue(), 'abc')
-
-    def test_writelines_error(self):
-        def errorGen():
-            yield 'a'
-            raise KeyboardInterrupt()
-        f = self.CLASS()
-        self.assertRaises(KeyboardInterrupt, f.writelines, errorGen())
-
-    def test_truncate(self):
-        eq = self.assertEqual
-        f = self.CLASS()
-        f.write(self._lines)
-        f.seek(10)
-        f.truncate()
-        eq(f.getvalue(), 'abcdefghij')
-        f.truncate(5)
-        eq(f.getvalue(), 'abcde')
-        f.write('xyz')
-        eq(f.getvalue(), 'abcdexyz')
-        self.assertRaises(ValueError, f.truncate, -1)
-        f.close()
-        self.assertRaises(ValueError, f.write, 'frobnitz')
-
-    def test_closed_flag(self):
-        f = self.CLASS()
-        self.assertEqual(f.closed, False)
-        f.close()
-        self.assertEqual(f.closed, True)
-        f = self.CLASS(self.constructor("abc"))
-        self.assertEqual(f.closed, False)
-        f.close()
-        self.assertEqual(f.closed, True)
-
-    def test_isatty(self):
-        f = self.CLASS()
-        self.assertRaises(TypeError, f.isatty, None)
-        self.assertEqual(f.isatty(), False)
-        f.close()
-        self.assertRaises(ValueError, f.isatty)
-
-    def test_iterator(self):
-        eq = self.assertEqual
-        unless = self.failUnless
-        eq(iter(self._fp), self._fp)
-        # Does this object support the iteration protocol?
-        unless(hasattr(self._fp, '__iter__'))
-        unless(hasattr(self._fp, '__next__'))
-        i = 0
-        for line in self._fp:
-            eq(line, self._line + '\n')
-            i += 1
-        eq(i, 5)
-        self._fp.close()
-        self.assertRaises(StopIteration, next, self._fp)
-
-class TestioStringIO(TestGenericStringIO, unittest.TestCase):
-    CLASS = io.StringIO
-
-    def test_unicode(self):
-
-        if not test_support.have_unicode: return
-
-        # The StringIO module also supports concatenating Unicode
-        # snippets to larger Unicode strings. This is tested by this
-        # method. Note that cStringIO does not support this extension.
-
-        f = self.CLASS()
-        f.write(self._line[:6])
-        f.seek(3)
-        f.write(str(self._line[20:26]))
-        f.write(str(self._line[52]))
-        s = f.getvalue()
-        self.assertEqual(s, str('abcuvwxyz!'))
-        self.assertEqual(type(s), str)
-
-
-def test_main():
-    test_support.run_unittest(TestioStringIO)
-
-
-if __name__ == '__main__':
-    test_main()
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index ba3ceeb..fa3a8bb 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -98,7 +98,7 @@ class IOTest(unittest.TestCase):
         self.assertEqual(f.seek(-1, 2), 13)
         self.assertEqual(f.tell(), 13)
         self.assertEqual(f.truncate(12), 12)
-        self.assertEqual(f.tell(), 13)
+        self.assertEqual(f.tell(), 12)
         self.assertRaises(TypeError, f.seek, 0.0)
 
     def read_ops(self, f, buffered=False):
@@ -143,7 +143,7 @@ class IOTest(unittest.TestCase):
         self.assertEqual(f.tell(), self.LARGE + 2)
         self.assertEqual(f.seek(0, 2), self.LARGE + 2)
         self.assertEqual(f.truncate(self.LARGE + 1), self.LARGE + 1)
-        self.assertEqual(f.tell(), self.LARGE + 2)
+        self.assertEqual(f.tell(), self.LARGE + 1)
         self.assertEqual(f.seek(0, 2), self.LARGE + 1)
         self.assertEqual(f.seek(-1, 2), self.LARGE)
         self.assertEqual(f.read(2), b"x")
@@ -727,6 +727,7 @@ class TextIOWrapperTest(unittest.TestCase):
             txt.write("BB\nCCC\n")
             txt.write("X\rY\r\nZ")
             txt.flush()
+            self.assertEquals(buf.closed, False)
             self.assertEquals(buf.getvalue(), expected)
 
     def testNewlines(self):
@@ -807,7 +808,8 @@ class TextIOWrapperTest(unittest.TestCase):
                 txt = io.TextIOWrapper(buf, encoding="ascii", newline=newline)
                 txt.write(data)
                 txt.close()
-                self.assertEquals(buf.getvalue(), expected)
+                self.assertEquals(buf.closed, True)
+                self.assertRaises(ValueError, buf.getvalue)
         finally:
             os.linesep = save_linesep
 
diff --git a/Lib/test/test_largefile.py b/Lib/test/test_largefile.py
index 4cafe33..0856346 100644
--- a/Lib/test/test_largefile.py
+++ b/Lib/test/test_largefile.py
@@ -120,14 +120,15 @@ class TestCase(unittest.TestCase):
             newsize -= 1
             f.seek(42)
             f.truncate(newsize)
-            self.assertEqual(f.tell(), 42)       # else pointer moved
-            f.seek(0, 2)
             self.assertEqual(f.tell(), newsize)  # else wasn't truncated
+            f.seek(0, 2)
+            self.assertEqual(f.tell(), newsize)
             # XXX truncate(larger than true size) is ill-defined
             # across platform; cut it waaaaay back
             f.seek(0)
             f.truncate(1)
-            self.assertEqual(f.tell(), 0)       # else pointer moved
+            self.assertEqual(f.tell(), 1)       # else pointer moved
+            f.seek(0)
             self.assertEqual(len(f.read()), 1)  # else wasn't truncated
 
 def test_main():
diff --git a/Lib/test/test_memoryio.py b/Lib/test/test_memoryio.py
new file mode 100644
index 0000000..0b09ca4
--- /dev/null
+++ b/Lib/test/test_memoryio.py
@@ -0,0 +1,405 @@
+"""Unit tests for memory-based file-like objects.
+StringIO -- for unicode strings
+BytesIO -- for bytes
+"""
+
+import unittest
+from test import test_support
+
+import io
+
+try:
+    import _bytesio
+    has_c_implementation = True
+except ImportError:
+    has_c_implementation = False
+
+
+class MemoryTestMixin:
+
+    def write_ops(self, f, t):
+        self.assertEqual(f.write(t("blah.")), 5)
+        self.assertEqual(f.seek(0), 0)
+        self.assertEqual(f.write(t("Hello.")), 6)
+        self.assertEqual(f.tell(), 6)
+        self.assertEqual(f.seek(5), 5)
+        self.assertEqual(f.tell(), 5)
+        self.assertEqual(f.write(t(" world\n\n\n")), 9)
+        self.assertEqual(f.seek(0), 0)
+        self.assertEqual(f.write(t("h")), 1)
+        self.assertEqual(f.truncate(12), 12)
+        self.assertEqual(f.tell(), 12)
+
+    def test_write(self):
+        buf = self.buftype("hello world\n")
+        memio = self.ioclass(buf)
+
+        self.write_ops(memio, self.buftype)
+        self.assertEqual(memio.getvalue(), buf)
+        memio = self.ioclass()
+        self.write_ops(memio, self.buftype)
+        self.assertEqual(memio.getvalue(), buf)
+        self.assertRaises(TypeError, memio.write, None)
+        memio.close()
+        self.assertRaises(ValueError, memio.write, self.buftype(""))
+
+    def test_writelines(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass()
+
+        self.assertEqual(memio.writelines([buf] * 100), None)
+        self.assertEqual(memio.getvalue(), buf * 100)
+        memio.writelines([])
+        self.assertEqual(memio.getvalue(), buf * 100)
+        memio = self.ioclass()
+        self.assertRaises(TypeError, memio.writelines, [buf] + [1])
+        self.assertEqual(memio.getvalue(), buf)
+        self.assertRaises(TypeError, memio.writelines, None)
+        memio.close()
+        self.assertRaises(ValueError, memio.writelines, [])
+
+    def test_writelines_error(self):
+        memio = self.ioclass()
+        def error_gen():
+            yield self.buftype('spam')
+            raise KeyboardInterrupt
+
+        self.assertRaises(KeyboardInterrupt, memio.writelines, error_gen())
+
+    def test_truncate(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+
+        self.assertRaises(ValueError, memio.truncate, -1)
+        memio.seek(6)
+        self.assertEqual(memio.truncate(), 6)
+        self.assertEqual(memio.getvalue(), buf[:6])
+        self.assertEqual(memio.truncate(4), 4)
+        self.assertEqual(memio.getvalue(), buf[:4])
+        self.assertEqual(memio.tell(), 4)
+        memio.write(buf)
+        self.assertEqual(memio.getvalue(), buf[:4] + buf)
+        pos = memio.tell()
+        self.assertEqual(memio.truncate(None), pos)
+        self.assertEqual(memio.tell(), pos)
+        self.assertRaises(TypeError, memio.truncate, '0')
+        memio.close()
+        self.assertRaises(ValueError, memio.truncate, 0)
+
+    def test_init(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+        self.assertEqual(memio.getvalue(), buf)
+        memio = self.ioclass(None)
+        self.assertEqual(memio.getvalue(), self.EOF)
+        memio.__init__(buf * 2)
+        self.assertEqual(memio.getvalue(), buf * 2)
+        memio.__init__(buf)
+        self.assertEqual(memio.getvalue(), buf)
+
+    def test_read(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+
+        self.assertEqual(memio.read(0), self.EOF)
+        self.assertEqual(memio.read(1), buf[:1])
+        self.assertEqual(memio.read(4), buf[1:5])
+        self.assertEqual(memio.read(900), buf[5:])
+        self.assertEqual(memio.read(), self.EOF)
+        memio.seek(0)
+        self.assertEqual(memio.read(), buf)
+        self.assertEqual(memio.read(), self.EOF)
+        self.assertEqual(memio.tell(), 10)
+        memio.seek(0)
+        self.assertEqual(memio.read(-1), buf)
+        memio.seek(0)
+        self.assertEqual(memio.read(None), buf)
+        self.assertRaises(TypeError, memio.read, '')
+        memio.close()
+        self.assertRaises(ValueError, memio.read)
+
+    def test_readline(self):
+        buf = self.buftype("1234567890\n")
+        memio = self.ioclass(buf * 2)
+
+        self.assertEqual(memio.readline(0), self.EOF)
+        self.assertEqual(memio.readline(), buf)
+        self.assertEqual(memio.readline(), buf)
+        self.assertEqual(memio.readline(), self.EOF)
+        memio.seek(0)
+        self.assertEqual(memio.readline(5), buf[:5])
+        self.assertEqual(memio.readline(5), buf[5:10])
+        self.assertEqual(memio.readline(5), buf[10:15])
+        memio.seek(0)
+        self.assertEqual(memio.readline(-1), buf)
+        memio.seek(0)
+        self.assertEqual(memio.readline(0), self.EOF)
+
+        buf = self.buftype("1234567890\n")
+        memio = self.ioclass((buf * 3)[:-1])
+        self.assertEqual(memio.readline(), buf)
+        self.assertEqual(memio.readline(), buf)
+        self.assertEqual(memio.readline(), buf[:-1])
+        self.assertEqual(memio.readline(), self.EOF)
+        memio.seek(0)
+        self.assertEqual(memio.readline(None), buf)
+        self.assertRaises(TypeError, memio.readline, '')
+        memio.close()
+        self.assertRaises(ValueError,  memio.readline)
+
+    def test_readlines(self):
+        buf = self.buftype("1234567890\n")
+        memio = self.ioclass(buf * 10)
+
+        self.assertEqual(memio.readlines(), [buf] * 10)
+        memio.seek(5)
+        self.assertEqual(memio.readlines(), [buf[5:]] + [buf] * 9)
+        memio.seek(0)
+        self.assertEqual(memio.readlines(15), [buf] * 2)
+        memio.seek(0)
+        self.assertEqual(memio.readlines(-1), [buf] * 10)
+        memio.seek(0)
+        self.assertEqual(memio.readlines(0), [buf] * 10)
+        memio.seek(0)
+        self.assertEqual(memio.readlines(None), [buf] * 10)
+        self.assertRaises(TypeError, memio.readlines, '')
+        memio.close()
+        self.assertRaises(ValueError, memio.readlines)
+
+    def test_iterator(self):
+        buf = self.buftype("1234567890\n")
+        memio = self.ioclass(buf * 10)
+
+        self.assertEqual(iter(memio), memio)
+        self.failUnless(hasattr(memio, '__iter__'))
+        self.failUnless(hasattr(memio, '__next__'))
+        i = 0
+        for line in memio:
+            self.assertEqual(line, buf)
+            i += 1
+        self.assertEqual(i, 10)
+        memio.seek(0)
+        i = 0
+        for line in memio:
+            self.assertEqual(line, buf)
+            i += 1
+        self.assertEqual(i, 10)
+        memio = self.ioclass(buf * 2)
+        memio.close()
+        self.assertRaises(ValueError, memio.__next__)
+
+    def test_getvalue(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+
+        self.assertEqual(memio.getvalue(), buf)
+        memio.read()
+        self.assertEqual(memio.getvalue(), buf)
+        memio = self.ioclass(buf * 1000)
+        self.assertEqual(memio.getvalue()[-3:], self.buftype("890"))
+        memio = self.ioclass(buf)
+        memio.close()
+        self.assertRaises(ValueError, memio.getvalue)
+
+    def test_seek(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+
+        memio.read(5)
+        self.assertRaises(ValueError, memio.seek, -1)
+        self.assertRaises(ValueError, memio.seek, 1, -1)
+        self.assertRaises(ValueError, memio.seek, 1, 3)
+        self.assertEqual(memio.seek(0), 0)
+        self.assertEqual(memio.seek(0, 0), 0)
+        self.assertEqual(memio.read(), buf)
+        self.assertEqual(memio.seek(3), 3)
+        self.assertEqual(memio.seek(0, 1), 3)
+        self.assertEqual(memio.read(), buf[3:])
+        self.assertEqual(memio.seek(len(buf)), len(buf))
+        self.assertEqual(memio.read(), self.EOF)
+        memio.seek(len(buf) + 1)
+        self.assertEqual(memio.read(), self.EOF)
+        self.assertEqual(memio.seek(0, 2), len(buf))
+        self.assertEqual(memio.read(), self.EOF)
+        memio.close()
+        self.assertRaises(ValueError, memio.seek, 0)
+
+    def test_overseek(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+
+        self.assertEqual(memio.seek(len(buf) + 1), 11)
+        self.assertEqual(memio.read(), self.EOF)
+        self.assertEqual(memio.tell(), 11)
+        self.assertEqual(memio.getvalue(), buf)
+        memio.write(self.EOF)
+        self.assertEqual(memio.getvalue(), buf)
+        memio.write(buf)
+        self.assertEqual(memio.getvalue(), buf + self.buftype('\0') + buf)
+
+    def test_tell(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+
+        self.assertEqual(memio.tell(), 0)
+        memio.seek(5)
+        self.assertEqual(memio.tell(), 5)
+        memio.seek(10000)
+        self.assertEqual(memio.tell(), 10000)
+        memio.close()
+        self.assertRaises(ValueError, memio.tell)
+
+    def test_flush(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+
+        self.assertEqual(memio.flush(), None)
+
+    def test_flags(self):
+        memio = self.ioclass()
+
+        self.assertEqual(memio.writable(), True)
+        self.assertEqual(memio.readable(), True)
+        self.assertEqual(memio.seekable(), True)
+        self.assertEqual(memio.isatty(), False)
+        self.assertEqual(memio.closed, False)
+        memio.close()
+        self.assertEqual(memio.writable(), True)
+        self.assertEqual(memio.readable(), True)
+        self.assertEqual(memio.seekable(), True)
+        self.assertRaises(ValueError, memio.isatty)
+        self.assertEqual(memio.closed, True)
+
+    def test_subclassing(self):
+        buf = self.buftype("1234567890")
+        def test1():
+            class MemIO(self.ioclass):
+                pass
+            m = MemIO(buf)
+            return m.getvalue()
+        def test2():
+            class MemIO(self.ioclass):
+                def __init__(me, a, b):
+                    self.ioclass.__init__(me, a)
+            m = MemIO(buf, None)
+            return m.getvalue()
+        self.assertEqual(test1(), buf)
+        self.assertEqual(test2(), buf)
+
+
+class PyBytesIOTest(MemoryTestMixin, unittest.TestCase):
+    @staticmethod
+    def buftype(s):
+        return s.encode("ascii")
+    ioclass = io._BytesIO
+    EOF = b""
+
+    def test_read1(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+
+        self.assertRaises(TypeError, memio.read1)
+        self.assertEqual(memio.read(), buf)
+
+    def test_readinto(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+
+        b = bytearray(b"hello")
+        self.assertEqual(memio.readinto(b), 5)
+        self.assertEqual(b, b"12345")
+        self.assertEqual(memio.readinto(b), 5)
+        self.assertEqual(b, b"67890")
+        self.assertEqual(memio.readinto(b), 0)
+        self.assertEqual(b, b"67890")
+        b = bytearray(b"hello world")
+        memio.seek(0)
+        self.assertEqual(memio.readinto(b), 10)
+        self.assertEqual(b, b"1234567890d")
+        b = bytearray(b"")
+        memio.seek(0)
+        self.assertEqual(memio.readinto(b), 0)
+        self.assertEqual(b, b"")
+        self.assertRaises(TypeError, memio.readinto, '')
+        import array
+        a = array.array('b', b"hello world")
+        memio = self.ioclass(buf)
+        memio.readinto(a)
+        self.assertEqual(a.tostring(), b"1234567890d")
+        memio.close()
+        self.assertRaises(ValueError, memio.readinto, b)
+
+    def test_relative_seek(self):
+        buf = self.buftype("1234567890")
+        memio = self.ioclass(buf)
+
+        self.assertEqual(memio.seek(-1, 1), 0)
+        self.assertEqual(memio.seek(3, 1), 3)
+        self.assertEqual(memio.seek(-4, 1), 0)
+        self.assertEqual(memio.seek(-1, 2), 9)
+        self.assertEqual(memio.seek(1, 1), 10)
+        self.assertEqual(memio.seek(1, 2), 11)
+        memio.seek(-3, 2)
+        self.assertEqual(memio.read(), buf[-3:])
+        memio.seek(0)
+        memio.seek(1, 1)
+        self.assertEqual(memio.read(), buf[1:])
+
+    def test_unicode(self):
+        memio = self.ioclass()
+
+        self.assertRaises(TypeError, self.ioclass, "1234567890")
+        self.assertRaises(TypeError, memio.write, "1234567890")
+        self.assertRaises(TypeError, memio.writelines, ["1234567890"])
+
+    def test_bytes_array(self):
+        buf = b"1234567890"
+        import array
+        a = array.array('b', list(buf))
+        memio = self.ioclass(a)
+        self.assertEqual(memio.getvalue(), buf)
+        self.assertEqual(memio.write(a), 10)
+        self.assertEqual(memio.getvalue(), buf)
+
+
+class PyStringIOTest(MemoryTestMixin, unittest.TestCase):
+    buftype = str
+    ioclass = io.StringIO
+    EOF = ""
+
+    def test_relative_seek(self):
+        memio = self.ioclass()
+
+        self.assertRaises(IOError, memio.seek, -1, 1)
+        self.assertRaises(IOError, memio.seek, 3, 1)
+        self.assertRaises(IOError, memio.seek, -3, 1)
+        self.assertRaises(IOError, memio.seek, -1, 2)
+        self.assertRaises(IOError, memio.seek, 1, 1)
+        self.assertRaises(IOError, memio.seek, 1, 2)
+
+    # XXX: For the Python version of io.StringIO, this is highly
+    # dependent on the encoding used for the underlying buffer.
+    # def test_widechar(self):
+    #     buf = self.buftype("\U0002030a\U00020347")
+    #     memio = self.ioclass(buf)
+    #
+    #     self.assertEqual(memio.getvalue(), buf)
+    #     self.assertEqual(memio.write(buf), len(buf))
+    #     self.assertEqual(memio.tell(), len(buf))
+    #     self.assertEqual(memio.getvalue(), buf)
+    #     self.assertEqual(memio.write(buf), len(buf))
+    #     self.assertEqual(memio.tell(), len(buf) * 2)
+    #     self.assertEqual(memio.getvalue(), buf + buf)
+
+if has_c_implementation:
+    class CBytesIOTest(PyBytesIOTest):
+        ioclass = io.BytesIO
+
+def test_main():
+    tests = [PyBytesIOTest, PyStringIOTest]
+    if has_c_implementation:
+        tests.extend([CBytesIOTest])
+    test_support.run_unittest(*tests)
+
+if __name__ == '__main__':
+    test_main()
diff --git a/Lib/test/test_mimetools.py b/Lib/test/test_mimetools.py
index cf0e191..ef333f5 100644
--- a/Lib/test/test_mimetools.py
+++ b/Lib/test/test_mimetools.py
@@ -58,7 +58,7 @@ class MimeToolsTest(unittest.TestCase):
             s.add(nb)
 
     def test_message(self):
-        msg = mimetools.Message(io.StringIO(msgtext1))
+        msg = mimetools.Message(io.StringIO(str(msgtext1)))
         self.assertEqual(msg.gettype(), "text/plain")
         self.assertEqual(msg.getmaintype(), "text")
         self.assertEqual(msg.getsubtype(), "plain")