Remove __future__ imports from Python files

rm-future.py

#! /usr/bin/env python
"""Remove __future__ imports from Python files

Acts on *.py files in the current directory and all subdirectories.

Only removes lines in which all imported names are in KNOWN_FUTURES.

Public URL of this script:
https://gist.github.com/millerdev/f71648c1a9690cfca7c8b7c049867cfc
"""
import os
from os.path import join

FUTURE = "from __future__ import "
KNOWN_FUTURES = {
    "absolute_import",
    "division",
    "print_function",
    "unicode_literals",
    "with_statement",
}


def main():
    print("removing future imports from...")
    for dirpath, dirnames, filenames in os.walk("."):
        for name in list(dirnames):
            if name.startswith("."):
                dirnames.remove(name)
        for name in filenames:
            if name.endswith(".py"):
                rm_future(join(dirpath, name))

def rm_future(path):
    future = FUTURE
    lines = []
    found = False
    with open(path, encoding="utf-8") as f:
        for line in f:
            if future in line:
                if is_known_future(line):
                    found = True
                else:
                    print("skipping unknown future:", line.strip(), "in", path)
                    lines.append(line)
            else:
                lines.append(line)
    if found and lines:
        print(path)
        assert "\n" in lines[0], repr(lines[0])
        with open(path, encoding="utf-8", mode="w") as f:
            f.write("".join(lines))


def is_known_future(line):
    if "#" in line:
        line = line[:line.index("#")]
    names = {p.strip() for p in line.replace(FUTURE, "").split(",")}
    return not names - KNOWN_FUTURES


if __name__ == "__main__":
    main()