I've been getting into Python lately. One problem that I've encountered under Windows, is that input redirection doesn't work if you use the .py file association to run the script; e.g.:

 C:\> foo.py < input.txt

There's a well-known input redirection bug. The fix is to explicitly use python.exe to run the script.

A related problem for me was that stdin was opened as a text file, not a binary file, so \r bytes were being discarded from binary input files. The fix is to run python.exe -u (unbuffered binary input and output).

I didn't want to hardcode the path to python.exe in a batch file, so I came up with the following wrapper, which parses the output from assoc .py and ftype Python.File.

Just place this batch file in the same directory as foo.py and call it foo.bat.

 @setlocal
 @if (%_echo%)==()  set _echo=off
 @echo %_echo%

 :: You must explicitly invoke python.exe, rather than rely on the
 :: file association for .py, if you want stdin redirection to work.
 :: See http://mail.python.org/pipermail/python-bugs-list/2004-August/024920.html
 :: The -u flag to python.exe specifies unbuffered, binary stdin,
 :: so '\r\n' is not remapped to '\n'.
 call :FindPythonExe

 if "%PythonExe%"=="" (
     echo Can't find python.exe
     exit /B 1
 )

 :: Replace the extension of this batch file with .py: s/.bat$/.py/
 set PythonFile=%~dpn0.py

 "%PythonExe%" -u %PythonFile% %*
 goto :EOF

 ::
 :: Find python.exe in the path or via the .py association
 ::
 :FindPythonExe
 set PythonExe=
 :: Search for python.{cmd,bat,exe} in %PATH%
 for %%i in (cmd bat exe) do (
     if "%PythonExe%"=="" (
         for %%j in (python.%%i) do set PythonExe=%%~$PATH:j
     )
 )
 :: Extract path to python.exe from .py association
 if "%PythonExe%"=="" call :AssocPy2Exe
 goto :EOF

 ::
 :: Return the executable associated with .py in %PythonExe%
 ::
 :AssocPy2Exe
 call :AssocExtn2Exe .py
 set PythonExe=%_exe%
 goto :EOF

 ::
 :: Return the executable associated with file extension %1 in %_exe%
 ::
 :AssocExtn2Exe
 :: assoc .py -> .py=Python.File
 for /f "usebackq tokens=2 delims==" %%i in (`assoc %1`) do set _ftype=%%i

 :: ftype Python.File -> Python.File="C:\Python24\python.exe" "%1" %*
 :: Grab everything after the '='
 for /f "usebackq tokens=2 delims==" %%i in (`ftype %_ftype%`) do set _rhs=%%i

 :: Get the first token of the space-separated list
 for /f "tokens=1" %%i in ("%_rhs%") do set _exe=%%i
 goto :EOF

Now you can run foo.bat < bar.jpg with the expected results.

Enjoy!

Update 2007/01/03: The batchfile now searches %PATH% before looking up the .py association.

Update 2007/01/12: See here for a significantly improved batchfile and for py2cmd.