Make a few more tests pass with the new I/O library.

Fix the truncate() semantics -- it should not affect the current position.
Switch wave.py/chunk.py to struct.unpack_from() to support bytes.
Don't use writelines() on binary files (test_fileinput.py).

Lib/chunk.py

@@ -62,7 +62,7 @@ class Chunk:
         if len(self.chunkname) < 4:
             raise EOFError
         try:
-            self.chunksize = struct.unpack(strflag+'L', file.read(4))[0]
+            self.chunksize = struct.unpack_from(strflag+'L', file.read(4))[0]
         except struct.error:
             raise EOFError
         if inclheader:

Lib/io.py

@@ -551,8 +551,6 @@ class _MemoryIOMixin(BufferedIOBase):
     def truncate(self, pos=None):
         if pos is None:
             pos = self._pos
-        else:
-            self._pos = max(0, pos)
         del self._buffer[pos:]
         return pos
 

Lib/test/test_fileinput.py

@@ -18,7 +18,8 @@ from fileinput import FileInput, hook_encoded
 def writeTmp(i, lines, mode='w'):  # opening in text mode is the default
     name = TESTFN + str(i)
     f = open(name, mode)
-    f.writelines(lines)
+    for line in lines:
+        f.write(line)
     f.close()
     return name
 

Lib/test/test_io.py

@@ -93,7 +93,7 @@ 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(), 12)
+        self.assertEqual(f.tell(), 13)
 
     def read_ops(self, f, buffered=False):
         data = f.read(5)
@@ -135,7 +135,7 @@ 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 + 1)
+        self.assertEqual(f.tell(), self.LARGE + 2)
         self.assertEqual(f.seek(0, 2), self.LARGE + 1)
         self.assertEqual(f.seek(-1, 2), self.LARGE)
         self.assertEqual(f.read(2), b"x")

Lib/wave.py

@@ -256,9 +256,9 @@ class Wave_read:
     #
 
     def _read_fmt_chunk(self, chunk):
-        wFormatTag, self._nchannels, self._framerate, dwAvgBytesPerSec, wBlockAlign = struct.unpack('<hhllh', chunk.read(14))
+        wFormatTag, self._nchannels, self._framerate, dwAvgBytesPerSec, wBlockAlign = struct.unpack_from('<hhllh', chunk.read(14))
         if wFormatTag == WAVE_FORMAT_PCM:
-            sampwidth = struct.unpack('<h', chunk.read(2))[0]
+            sampwidth = struct.unpack_from('<h', chunk.read(2))[0]
             self._sampwidth = (sampwidth + 7) // 8
         else:
             raise Error, 'unknown format: %r' % (wFormatTag,)

Modules/_fileio.c

@@ -519,7 +519,7 @@ fileio_truncate(PyFileIOObject *self, PyObject *args)
 {
 	PyObject *posobj = NULL;
 	Py_off_t pos;
-	int fd, whence;
+	int fd;
 
 	fd = self->fd;
 	if (fd < 0)
@@ -530,17 +530,14 @@ fileio_truncate(PyFileIOObject *self, PyObject *args)
 	if (!PyArg_ParseTuple(args, "|O", &posobj))
 		return NULL;
 
-	if (posobj == Py_None)
-		posobj = NULL;
-
-	if (posobj == NULL)
-		whence = 1;
-	else
-		whence = 0;
-
-	posobj = portable_lseek(fd, posobj, whence);
-	if (posobj == NULL)
-		return NULL;
+	if (posobj == Py_None || posobj == NULL) {
+                posobj = portable_lseek(fd, NULL, 1);
+                if (posobj == NULL)
+                  return NULL;
+        }
+        else {
+		Py_INCREF(posobj);
+        }
 
 #if !defined(HAVE_LARGEFILE_SUPPORT)
 	pos = PyInt_AsLong(posobj);