in setupbase.py [0:0]
def which(cmd, mode=os.F_OK | os.X_OK, path=None):
"""Given a command, mode, and a PATH string, return the path which
conforms to the given mode on the PATH, or None if there is no such
file.
`mode` defaults to os.F_OK | os.X_OK. `path` defaults to the result
of os.environ.get("PATH"), or can be overridden with a custom search
path.
"""
# Check that a given file can be accessed with the correct mode.
# Additionally check that `file` is not a directory, as on Windows
# directories pass the os.access check.
def _access_check(fn, mode):
return (os.path.exists(fn) and os.access(fn, mode) and
not os.path.isdir(fn))
# Short circuit. If we're given a full path which matches the mode
# and it exists, we're done here.
if _access_check(cmd, mode):
return cmd
path = (path or os.environ.get("PATH", os.defpath)).split(os.pathsep)
if sys.platform == "win32":
# The current directory takes precedence on Windows.
if os.curdir not in path:
path.insert(0, os.curdir)
# PATHEXT is necessary to check on Windows.
pathext = os.environ.get("PATHEXT", "").split(os.pathsep)
# See if the given file matches any of the expected path extensions.
# This will allow us to short circuit when given "python.exe".
matches = [cmd for ext in pathext if cmd.lower().endswith(ext.lower())]
# If it does match, only test that one, otherwise we have to try
# others.
files = [cmd] if matches else [cmd + ext.lower() for ext in pathext]
else:
# On other platforms you don't have things like PATHEXT to tell you
# what file suffixes are executable, so just pass on cmd as-is.
files = [cmd]
seen = set()
for dir in path:
dir = os.path.normcase(dir)
if dir not in seen:
seen.add(dir)
for thefile in files:
name = os.path.join(dir, thefile)
if _access_check(name, mode):
return name
return None