Fix #444582. Add shutil.which function for finding programs on the system path.
diff --git a/Lib/shutil.py b/Lib/shutil.py
index 46398ef..a4c1436 100644
--- a/Lib/shutil.py
+++ b/Lib/shutil.py
@@ -36,7 +36,7 @@
"register_archive_format", "unregister_archive_format",
"get_unpack_formats", "register_unpack_format",
"unregister_unpack_format", "unpack_archive",
- "ignore_patterns", "chown"]
+ "ignore_patterns", "chown", "which"]
# disk_usage is added later, if available on the platform
class Error(EnvironmentError):
@@ -961,3 +961,51 @@
lines = size.lines
return os.terminal_size((columns, lines))
+
+def which(cmd, mode=os.F_OK | os.X_OK, path=None):
+ """Given a file, mode, and a path string, return the path whichs conform
+ to the given mode on the 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):
+ if (os.path.exists(fn) and os.access(fn, mode)
+ and not os.path.isdir(fn)):
+ return True
+ return False
+
+ # 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 not os.curdir 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 + ext.lower() for ext in pathext] if not matches else [cmd]
+ 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(os.path.abspath(dir))
+ if not dir in seen:
+ seen.add(dir)
+ for thefile in files:
+ name = os.path.join(dir, thefile)
+ if _access_check(name, mode):
+ return name
+ return None
+