subprocess.Popen stdin read file

Question

I\'m trying to call a process on a file after part of it has been read. For example:

with open(\'in.txt\', \'r\') as a, open(\'out.txt\', \'w\') as b:
  hea         


        

Answer 1

It happens because the subprocess module extracts the File handle from the File Object.

http://hg.python.org/releasing/2.7.6/file/ba31940588b6/Lib/subprocess.py

In line 1126, coming from 701.

The File Object uses buffers and has already read a lot from the file handle when the subprocess extracts it.