Installing Mods With Python (v 2.0)
I'll leave an in-depth analysis to the true Python experts, but here are just some quick notes:

Variable and function names: As far as I'm aware, variable and function names should have words/elements separated by underscores (e.g., check_dirs, is_file)

main() function: Instead of having your functionality on the first/default level of indentation, it's good form to wrap it in a def main() and call it via:

if __name__ == '__main__':
    main()


Return values: You can simply return a bool directly rather than having an if/else construction.  e.g.,

return isfile != len(os.listdir(target))


vs.

if isfile == len(os.listdir(target)):
    return False
else:
    return True


Use of global: In my experience, any time I have to use global some_var, it's indicative of bad design.  You should either be using local variables, function arguments, or the constant should be well-defined and not hidden by any local fields.