Add line_buffering to TextIOWrapper().

pep-3116.txt

@@ -339,7 +339,8 @@ object.  Each ``TextIOWrapper`` object has a property named
 ``BufferedIOBase`` object.  Its initializer has the following
 signature:
 
-    ``.__init__(self, buffer, encoding=None, errors=None, newline=None)``
+    ``.__init__(self, buffer, encoding=None, errors=None, newline=None,
+                line_buffering=False)``
 
         ``buffer`` is a reference to the ``BufferedIOBase`` object to
         be wrapped with the ``TextIOWrapper``.
@@ -377,6 +378,12 @@ signature:
           guiding translation are different for output than for
           input.)
 
+        ``line_buffering``, if True, causes ``write()`` calls to imply
+        a ``flush()`` if the string written contains at least one
+        ``'\n'`` or ``'\r'`` character.  This is set by ``open()``
+        when it detects that the underlying stream is a TTY device,
+        or when a ``buffering`` argument of ``1`` is passed.
+
         Further notes on the ``newline`` parameter:
 
         * ``'\r'`` support is still needed for some OSX applications
@@ -487,7 +494,8 @@ pseudo-code::
             raise ValueError("binary modes doesn't take a newline arg")
         # XXX Need to spec the signature for FileIO()
         raw = FileIO(filename, mode)
-        if buffering is None:
+        line_buffering = (buffering == 1 or buffering is None and raw.isatty())
+        if line_buffering or buffering is None:
             buffering = 8*1024  # International standard buffer size
             # XXX Try setting it to fstat().st_blksize
         if buffering < 0:
@@ -506,7 +514,7 @@ pseudo-code::
         if binary:
             return buffer
         assert text
-        return TextIOWrapper(buffer, encoding, errors, newline)
+        return TextIOWrapper(buffer, encoding, errors, newline, line_buffering)
 
 
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