tabstospaces.py

#!/usr/bin/env python
import argparse
import ast
import re
import sys

TS = 4

def process_match(match):
    col = 0
    for c in match.group(0):
        if c == " ":
            col += 1
        elif c == "\t":
            col = col - col % TS + TS
        elif c == "\n":
            return "\n"
        else:
            raise ValueError("Unknown character %r" % c)
    return " " * col

def process_line(line):
    return re.sub(r"^\s*", process_match, line)

def process_file(filename):
    with open(filename) as f:
        lines = f.readlines()
    old_ast = ast.parse("".join(lines), filename)
    lines = map(process_line, lines)
    new_ast = ast.parse("".join(lines), filename)
    if ast.dump(old_ast) == ast.dump(new_ast):
        with open(filename, "w") as f:
            f.writelines(lines)
    else:
        print >> sys.stdout, "%s: Not writing changes because AST would change."
        return False
    return True

def main():
    arg_parser = argparse.ArgumentParser(
        description="Uber-tabs-to-spaces converter for Python source code.")

    arg_parser.add_argument("filename", nargs=argparse.REMAINDER, help="file to process")
    args = arg_parser.parse_args()

    ret = 0
    for filename in args.filename:
        if not process_file(filename):
            ret = 1
    return ret

if __name__ == '__main__':
    sys.exit(main())