which.py

import os
import sys


def which(command):
    paths = os.getenv('PATH', '').split(os.pathsep)
    for path in paths:
        possible_command = os.path.join(path, command)
        is_valid_command = os.path.isfile(possible_command) and \
            os.access(possible_command, os.X_OK)
        if is_valid_command:
            return possible_command


if __name__ == '__main__':
    success = True
    for command in sys.argv[1:]:
        found = which(command)
        if found:
            print(found)
        else:
            success = False
    sys.exit(not success)