add_future_imports.py

from __future__ import absolute_import, division, unicode_literals

import os


def get_py_files():
    for path, folders, files in os.walk('./'):
        for filename in files:
            if filename.endswith('.py'):
                yield path + '/' + filename


def process_file(filename):
    with open(filename, 'r') as py_file:
        lines = py_file.readlines()

    if not lines:
        return

    start_index = 0
    while True:
        if lines[start_index].startswith('#'):
            start_index += 1
        else:
            break

    # clean empty lines at the top of the file and existing future imports as it's much simpler than modify existing :)
    while True:
        line = lines[start_index]
        if line == '\n' or '__future__' in line:
            del lines[start_index]
        else:
            break

    lines.insert(start_index, 'from __future__ import absolute_import, division, unicode_literals\n')
    lines.insert(start_index + 1, '\n')

    with open(filename, 'w') as py_file:
        py_file.writelines(lines)


if __name__ == '__main__':
    for py_file_name in get_py_files():
        process_file(py_file_name)