How is it possible to use raw_input() in a Python Git hook?

I am writing a pre-commit hook for Git that runs pyflakes and checks for tabs and trailing spaces in the modified files (code on Github). I would like to make it possible to override the hook by asking for user confirmation as follows:

answer = raw_input('Commit anyway? [N/y] ')
if answer.strip()[0].lower() == 'y':
    print >> sys.stderr, 'Committing anyway.'
    sys.exit(0)
else:
    print >> sys.stderr, 'Commit aborted.'
    sys.exit(1)

This code produces an error:

Commit anyway? [N/y] Traceback (m开发者_运维问答ost recent call last):
  File ".git/hooks/pre-commit", line 59, in ?
    main()
  File ".git/hooks/pre-commit", line 20, in main
    answer = raw_input('Commit anyway? [N/y] ')
EOFError: EOF when reading a line

Is it even possible to use raw_input() or a similar function in Git hooks and if yes, what am I doing wrong?

You could use:

sys.stdin = open('/dev/tty')
answer = raw_input('Commit anyway? [N/y] ')
if answer.strip().lower().startswith('y'):
    ...

git commit calls python .git/hooks/pre-commit:

% ps axu
...
unutbu   21801  0.0  0.1   6348  1520 pts/1    S+   17:44   0:00 git commit -am line 5a
unutbu   21802  0.1  0.2   5708  2944 pts/1    S+   17:44   0:00 python .git/hooks/pre-commit

Looking inside /proc/21802/fd (on this linux box) shows the state of the file descriptors for the process with PID 21802 (the pre-commit process):

  /proc/21802/fd:
  lrwx------ 1 unutbu unutbu 64 2011-09-15 17:45 0 -> /dev/null
  lrwx------ 1 unutbu unutbu 64 2011-09-15 17:45 1 -> /dev/pts/1
  lrwx------ 1 unutbu unutbu 64 2011-09-15 17:45 2 -> /dev/pts/1
  lr-x------ 1 unutbu unutbu 64 2011-09-15 17:45 3 -> /dev/tty
  lr-x------ 1 unutbu unutbu 64 2011-09-15 17:45 5 -> /dev/null

Thus, pre-commit was spawned with sys.stdin pointing at /dev/null. sys.stdin = open('/dev/tty') redirects sys.stdin to an open filehandle from which raw_input can read.

In shell you can:

read ANSWER < /dev/tty