Implement long positioning (Unix only, probably).

Etc., etc.

2 files changed, 59 insertions, 44 deletions

diff --git a/Lib/io.py b/Lib/io.py
index 9f2a647..69c6c20 100644
--- a/Lib/io.py
+++ b/Lib/io.py
@@ -1,9 +1,15 @@
-"""New I/O library.
+"""New I/O library conforming to PEP 3116.
 
 This is an early prototype; eventually some of this will be
 reimplemented in C and the rest may be turned into a package.
 
-See PEP 3116.
+Conformance of alternative implementations: all arguments are intended
+to be positional-only except the arguments of the open() function.
+Argument names except those of the open() function are not part of the
+specification.  Instance variables and methods whose name starts with
+a leading underscore are not part of the specification (except "magic"
+names like __iter__).  Only the top-level names listed in the __all__
+variable are part of the specification.
 
 XXX need to default buffer size to 1 if isatty()
 XXX need to support 1 meaning line-buffered
@@ -142,6 +148,9 @@ class IOBase:
 
     This does not define read(), readinto() and write(), nor
     readline() and friends, since their signatures vary per layer.
+
+    Not that calling any method (even inquiries) on a closed file is
+    undefined.  Implementations may raise IOError in this case.
     """
 
     ### Internal ###
@@ -153,19 +162,20 @@ class IOBase:
 
     ### Positioning ###
 
-    def seek(self, pos: int, whence: int = 0) -> None:
-        """seek(pos: int, whence: int = 0) -> None.  Change stream position.
+    def seek(self, pos: int, whence: int = 0) -> int:
+        """seek(pos: int, whence: int = 0) -> int.  Change stream position.
 
         Seek to byte offset pos relative to position indicated by whence:
              0  Start of stream (the default).  pos should be >= 0;
              1  Current position - whence may be negative;
              2  End of stream - whence usually negative.
+        Returns the new absolute position.
         """
         self._unsupported("seek")
 
     def tell(self) -> int:
         """tell() -> int.  Return current stream position."""
-        self._unsupported("tell")
+        return self.seek(0, 1)
 
     def truncate(self, pos: int = None) -> None:
         """truncate(size: int = None) -> None. Truncate file to size bytes.
@@ -432,7 +442,7 @@ class _BufferedIOMixin(BufferedIOBase):
     ### Positioning ###
 
     def seek(self, pos, whence=0):
-        self.raw.seek(pos, whence)
+        return self.raw.seek(pos, whence)
 
     def tell(self):
         return self.raw.tell()
@@ -515,6 +525,7 @@ class _MemoryIOMixin(BufferedIOBase):
             self._pos = max(0, len(self._buffer) + pos)
         else:
             raise IOError("invalid whence value")
+        return self._pos
 
     def tell(self):
         return self._pos
@@ -620,8 +631,9 @@ class BufferedReader(_BufferedIOMixin):
     def seek(self, pos, whence=0):
         if whence == 1:
             pos -= len(self._read_buf)
-        self.raw.seek(pos, whence)
+        pos = self.raw.seek(pos, whence)
         self._read_buf = b""
+        return pos
 
 
 class BufferedWriter(_BufferedIOMixin):
@@ -679,7 +691,7 @@ class BufferedWriter(_BufferedIOMixin):
 
     def seek(self, pos, whence=0):
         self.flush()
-        self.raw.seek(pos, whence)
+        return self.raw.seek(pos, whence)
 
 
 class BufferedRWPair(BufferedIOBase):
@@ -750,13 +762,9 @@ class BufferedRandom(BufferedWriter, BufferedReader):
         self.flush()
         # First do the raw seek, then empty the read buffer, so that
         # if the raw seek fails, we don't lose buffered data forever.
-        self.raw.seek(pos, whence)
+        pos = self.raw.seek(pos, whence)
         self._read_buf = b""
-        # XXX I suppose we could implement some magic here to move through the
-        # existing read buffer in the case of seek(<some small +ve number>, 1)
-        # XXX OTOH it might be good to *guarantee* that the buffer is
-        # empty after a seek or flush; for small relative forward
-        # seeks one might as well use small reads instead.
+        return pos
 
     def tell(self):
         if (self._write_buf):
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 2ca1e70..87d6df6 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -4,10 +4,10 @@ import unittest
 from itertools import chain
 from test import test_support
 
-import io
+import io  # The module under test
 
 
-class MockIO(io.RawIOBase):
+class MockRawIO(io.RawIOBase):
 
     def __init__(self, read_stack=()):
         self._read_stack = list(read_stack)
@@ -56,13 +56,13 @@ class MockFileIO(io.BytesIO):
 
 class MockNonBlockWriterIO(io.RawIOBase):
 
-    def __init__(self, blockingScript):
-        self.bs = list(blockingScript)
+    def __init__(self, blocking_script):
+        self._blocking_script = list(blocking_script)
         self._write_stack = []
 
     def write(self, b):
         self._write_stack.append(b[:])
-        n = self.bs.pop(0)
+        n = self._blocking_script.pop(0)
         if (n < 0):
             raise io.BlockingIOError(0, "test blocking", -n)
         else:
@@ -90,6 +90,23 @@ class IOTest(unittest.TestCase):
         f.seek(-2, 2)
         f.truncate()
 
+    def large_file_ops(self, f):
+        assert f.readable()
+        assert f.writable()
+        self.assertEqual(f.seek(2**32), 2**32)
+        self.assertEqual(f.tell(), 2**32)
+        self.assertEqual(f.write(b"xxx"), 3)
+        self.assertEqual(f.tell(), 2**32 + 3)
+        self.assertEqual(f.seek(-1, 1), 2**32 + 2)
+        f.truncate()
+        self.assertEqual(f.tell(), 2**32 + 2)
+        self.assertEqual(f.seek(0, 2), 2**32 + 2)
+        f.truncate(2**32 + 1)
+        self.assertEqual(f.tell(), 2**32 + 1)
+        self.assertEqual(f.seek(0, 2), 2**32 + 1)
+        self.assertEqual(f.seek(-1, 2), 2**32)
+        self.assertEqual(f.read(2), b"x")
+
     def read_ops(self, f):
         data = f.read(5)
         self.assertEqual(data, b"hello")
@@ -130,19 +147,9 @@ class IOTest(unittest.TestCase):
         f = io.BytesIO(data)
         self.read_ops(f)
 
-    def test_fileio_FileIO(self):
-        import _fileio
-        f = _fileio._FileIO(test_support.TESTFN, "w")
-        self.assertEqual(f.readable(), False)
-        self.assertEqual(f.writable(), True)
-        self.assertEqual(f.seekable(), True)
-        self.write_ops(f)
-        f.close()
-        f = _fileio._FileIO(test_support.TESTFN, "r")
-        self.assertEqual(f.readable(), True)
-        self.assertEqual(f.writable(), False)
-        self.assertEqual(f.seekable(), True)
-        self.read_ops(f)
+    def test_large_file_ops(self):
+        f = io.open(test_support.TESTFN, "w+b", buffering=0)
+        self.large_file_ops(f)
         f.close()
 
 
@@ -205,7 +212,7 @@ class StringIOTest(MemorySeekTestMixin, unittest.TestCase):
 class BufferedReaderTest(unittest.TestCase):
 
     def testRead(self):
-        rawio = MockIO((b"abc", b"d", b"efg"))
+        rawio = MockRawIO((b"abc", b"d", b"efg"))
         bufio = io.BufferedReader(rawio)
 
         self.assertEquals(b"abcdef", bufio.read(6))
@@ -231,7 +238,7 @@ class BufferedReaderTest(unittest.TestCase):
 
     def testReadNonBlocking(self):
         # Inject some None's in there to simulate EWOULDBLOCK
-        rawio = MockIO((b"abc", b"d", None, b"efg", None, None))
+        rawio = MockRawIO((b"abc", b"d", None, b"efg", None, None))
         bufio = io.BufferedReader(rawio)
 
         self.assertEquals(b"abcd", bufio.read(6))
@@ -241,19 +248,19 @@ class BufferedReaderTest(unittest.TestCase):
         self.assertEquals(b"", bufio.read())
 
     def testReadToEof(self):
-        rawio = MockIO((b"abc", b"d", b"efg"))
+        rawio = MockRawIO((b"abc", b"d", b"efg"))
         bufio = io.BufferedReader(rawio)
 
         self.assertEquals(b"abcdefg", bufio.read(9000))
 
     def testReadNoArgs(self):
-        rawio = MockIO((b"abc", b"d", b"efg"))
+        rawio = MockRawIO((b"abc", b"d", b"efg"))
         bufio = io.BufferedReader(rawio)
 
         self.assertEquals(b"abcdefg", bufio.read())
 
     def testFileno(self):
-        rawio = MockIO((b"abc", b"d", b"efg"))
+        rawio = MockRawIO((b"abc", b"d", b"efg"))
         bufio = io.BufferedReader(rawio)
 
         self.assertEquals(42, bufio.fileno())
@@ -268,7 +275,7 @@ class BufferedWriterTest(unittest.TestCase):
 
     def testWrite(self):
         # Write to the buffered IO but don't overflow the buffer.
-        writer = MockIO()
+        writer = MockRawIO()
         bufio = io.BufferedWriter(writer, 8)
 
         bufio.write(b"abc")
@@ -276,7 +283,7 @@ class BufferedWriterTest(unittest.TestCase):
         self.assertFalse(writer._write_stack)
 
     def testWriteOverflow(self):
-        writer = MockIO()
+        writer = MockRawIO()
         bufio = io.BufferedWriter(writer, 8)
 
         bufio.write(b"abc")
@@ -305,13 +312,13 @@ class BufferedWriterTest(unittest.TestCase):
         # later.
 
     def testFileno(self):
-        rawio = MockIO((b"abc", b"d", b"efg"))
+        rawio = MockRawIO((b"abc", b"d", b"efg"))
         bufio = io.BufferedWriter(rawio)
 
         self.assertEquals(42, bufio.fileno())
 
     def testFlush(self):
-        writer = MockIO()
+        writer = MockRawIO()
         bufio = io.BufferedWriter(writer, 8)
 
         bufio.write(b"abc")
@@ -323,8 +330,8 @@ class BufferedWriterTest(unittest.TestCase):
 class BufferedRWPairTest(unittest.TestCase):
 
     def testRWPair(self):
-        r = MockIO(())
-        w = MockIO()
+        r = MockRawIO(())
+        w = MockRawIO()
         pair = io.BufferedRWPair(r, w)
 
         # XXX need implementation
@@ -333,7 +340,7 @@ class BufferedRWPairTest(unittest.TestCase):
 class BufferedRandomTest(unittest.TestCase):
 
     def testReadAndWrite(self):
-        raw = MockIO((b"asdf", b"ghjk"))
+        raw = MockRawIO((b"asdf", b"ghjk"))
         rw = io.BufferedRandom(raw, 8, 12)
 
         self.assertEqual(b"as", rw.read(2))