os.path.exists() for files in your Path?

Question

I commonly use os.path.exists() to check if a file is there before doing anything with it.

I\'ve run across a situation where I\'m calling a executable that

Answer 1

Extending Trey Stout's search with Carl Meyer's comment on PATHEXT:

import os
def exists_in_path(cmd):
  # can't search the path if a directory is specified
  assert not os.path.dirname(cmd)

  extensions = os.environ.get("PATHEXT", "").split(os.pathsep)
  for directory in os.environ.get("PATH", "").split(os.pathsep):
    base = os.path.join(directory, cmd)
    options = [base] + [(base + ext) for ext in extensions]
    for filename in options:
      if os.path.exists(filename):
        return True
  return False

EDIT: Thanks to Aviv (on my blog) I now know there's a Twisted implementation: twisted.python.procutils.which

EDIT: In Python 3.3 and up there's shutil.which() in the standard library.