fix_import.py

#!/usr/bin/env python3.6
"""Python replace absolute imports with relative ones.

HARDLY TESTED. Use at own risk.

Only works from imports of type "from ... import ...".
Doesn't fix indentation for multiline imports.

Usage: show changes:  ./fix_import.py package_directory
       write changes: ./fix_import.py package_directory write
"""
import glob
import os
import sys

pkg = sys.argv[1]

for fname in glob.glob(f'{pkg}/**/*.py', recursive=True):

    depth = len([x for x in fname if x == '/'])
    current_module = os.path.dirname(fname).split('/')

    with open(fname) as f:
        data = f.readlines()

    new_lines = []
    for line in data:
        if line.startswith(f'from {pkg}') and 'import' in line:
            print(line)
            _, abs_import, _, *targets = line.split(' ')
            target = ' '.join(targets)
            import_module = abs_import.split('.')
            n_match = 0
            for imp, cur in zip(import_module, current_module):
                if imp == cur:
                    n_match += 1
                else:
                    break
            not_matched = depth - n_match
            dots = '.' * (not_matched + 1)
            remaining_imports = '.'.join(import_module[n_match:])
            new_line = f'from {dots}{remaining_imports} import {target}'
            print('fixing\t', line.strip(), 'in', fname)
            print('\t', new_line)
        else:
            new_line = line
        new_lines.append(new_line)

    if len(sys.argv) == 3 and sys.argv[2] == 'write':
        with open(fname, 'w') as f:
            f.writelines(new_lines)