Make subprocess find git executable on Windows

Question

import subprocess
proc = subprocess.Popen('git status')
print 'result: ', proc.communicate()

I have git in my system path, but when I run subprocess like this I get:
WindowsError: [Error 2] The system cannot find the file specified

How can I get subprocess to find git in the system path?

Python 2.6 on Windows XP.

• aknuds1: The real problem isn't that subprocess isn't using PATH, but that git is installed as 'git.cmd', rather than 'git.exe', which would be found by subprocess.Popen.
• djvg: This occurred for me using subprocess.check_output(...) on windows 10 after updating git to 2.19.1. Worked before the update. Now does not even work with shell=True.

Answer 1

The problem you see here is that the Windows API function CreateProcess, used by subprocess under the hood, doesn't auto-resolve other executable extensions than .exe. On Windows, the 'git' command is really installed as git.cmd. Therefore, you should modify your example to explicitly invoke git.cmd:

import subprocess
proc = subprocess.Popen('git.cmd status')
print 'result: ', proc.communicate()

The reason git works when shell==True is that the Windows shell auto-resolves git to git.cmd.

Eventually, resolve git.cmd yourself:

import subprocess
import os.path
def resolve_path(executable):
 if os.path.sep in executable:
 raise ValueError("Invalid filename: %s" % executable)
 path = os.environ.get("PATH", "").split(os.pathsep)
 # PATHEXT tells us which extensions an executable may have
 path_exts = os.environ.get("PATHEXT", ".exe;.bat;.cmd").split(";")
 has_ext = os.path.splitext(executable)[1] in path_exts
 if not has_ext:
 exts = path_exts
 else:
 # Don't try to append any extensions
 exts = [""]
 for d in path:
 try:
 for ext in exts:
 exepath = os.path.join(d, executable + ext)
 if os.access(exepath, os.X_OK):
 return exepath
 except OSError:
 pass
 return None
git = resolve_path("git")
proc = subprocess.Popen('{0} status'.format(git))
print 'result: ', proc.communicate()

• Jesse Aldridge: Oh, ok. I'm not using Windows anymore, so I can't confirm this answer, but I'm just going to assume you're right. Thanks.
• joshua: Also check [this python bug report][1]. [1]: bugs.python.org/issue17023 "If you add a directory into PATH on Windows so that the directory is in quotes, subprocess does not find executables in it."
• Daira-Emma Hopwood: The environment variable that lists executable extensions is called PATHEXT, not PATHEXTS. (The code as given will always fall back to ".exe;.bat;.cmd", since PATHEXTS typically won't exist.)

Answer 2

You mean

proc = subprocess.Popen(["git", "status"], stdout=subprocess.PIPE)

The first argument of subprocess.Popen takes a shlex.split-like list of arguments.

or:

proc = subprocess.Popen("git status", stdout=subprocess.PIPE, shell=True)

This is not recommended, as you are launching a shell then launching a process in the shell.

Also, you should use stdout=subprocess.PIPE to retrieve the result.

• jdd: No, Popen takes either a string or a list. See docs.python.org/library/subprocess.html
• user193476: Depends -- if you have arguments, then you must use a list. Otherwise, you're just invoking "git status" and not git status.
• user193476: shell=True is required if you do not use a list of arguments.
• jdd: Oh lordy, you do indeed need shell=True if you're on Windows, maybe. See bugs.python.org/issue8557 . The discussion in the comments is enlightening,
• aknuds1: The reason that shell invocation works is simply that the shell auto-resolves 'git' against 'git.cmd', not just 'git.exe' like the Windows API does.

Answer 3

Note that in 2020, with With Git 2.28 (Q3 2020), Python 2.6 or older is no longer supported.

See commit 45a87a8 (07 Jun 2020) by Denton Liu (Denton-L).
^{(Merged by Junio C Hamano -- gitster -- in commit 6361eb7, 18 Jun 2020)}

CodingGuidelines: specify Python 2.7 is the oldest version

^{Signed-off-by: Denton Liu}

In 0b4396f068 ("git-p4: make python2.7 the oldest supported version", 2019年12月13日, Git v2.27.0-rc0 -- merge listed in batch #1), git-p4 was updated to only support 2.7 and newer. Since Python 2.6 is pretty much ancient history, update CodingGuidelines to show that 2.7 is the oldest version supported.

Answer 4

I believe you need to pass env in to Popen, something like:

import subprocess, os
proc = subprocess.Popen('git status', env=os.environ, stdout=subprocess.PIPE)

Should do the trick.

• aknuds1: The default env is equivalent to os.environ.