diff files quickly in subdirs

diff_files.py

#!/usr/bin/env python3

import os
import glob
import itertools
import sys
import argparse

from subprocess import Popen, PIPE

def parseargs():
    parser = argparse.ArgumentParser(description='quickly diff files in subdirs')
    parser.add_argument('filename', help="this is the file that you're looking for")
    parser.add_argument('--exclude', dest="excluded", action="append",
                        help="pass in a string to exclude dirs with that string")
    parser.add_argument('--only', dest="only", action="append",
                        help="pass in a string to include only dirs with that string")

    return parser.parse_args()

def gen_dirs(fn, exclude_list=None, only_list=None):
    if exclude_list is None:
        exclude_list =[]
    if only_list is None:
        only_list =[]

    return (d for d in glob.iglob('*')
            if os.path.isdir(d)
            and filter_dir_names(d, exclude_list, only_list)
            and os.path.exists(os.path.join('.', d, fn)))

def filter_dir_names(d, exclude_list=None, only_list=None):
    if exclude_list is None:
        exclude_list =[]
    if only_list is None:
        only_list =['']
    only =  any(s in d for s in only_list) if only_list else True
    exclude =  any(s in d for s in exclude_list) if exclude_list else True
    return only and not exclude


def filename_writer(fn, excluded=None, only=None):
    if excluded is None:
        excluded = []
    if only is None:
        only = []

    exclude_str = ('-'.join(['','excluding',*excluded])) if excluded else ''
    include_str = ('-'.join(['','including', *only])) if only else ''
    return f"diff-{fn}-report{include_str}{exclude_str}.txt"

def filter_list_to_str(f_list):
    ret_str = ""
    if len(f_list)==1:
        ret_str+=f_list[0]
    elif len(f_list)==2:
        ret_str+=" and ".join(f_list)
    elif len(f_list)>2:
        ret_str+=f"{', '.join(f_list[:-1])}, and {f_list[-1]}"
    return ret_str

def main():
    parser = parseargs()
    fn = parser.filename
    excluded = parser.excluded
    only = parser.only
    dir_gen = gen_dirs(fn, exclude_list=excluded, only_list=only)
    output_file = filename_writer(fn, excluded, only)

    if os.path.exists(output_file):
        os.remove(output_file)
    to_write = []
    no_diff_dict = {}
    for d in itertools.combinations(dir_gen, 2):
        f1, f2 = map(lambda x: os.path.join(x, fn), d)
        d1, d2 = map(str, d)
        header = f"{f1} compared to {f2} is different as follows:"
        diff_cmd =['diff', f'{f1}', f'{f2}']
        p = Popen(diff_cmd, stdin=PIPE, stdout=PIPE, stderr=PIPE)
        output, err = p.communicate()
        if output:
            to_write.extend([header, f"{'-'*len(header)}"])
            to_write.append(f"{output.decode('utf-8')}\n")
        else:
            if d1 in no_diff_dict:
                no_diff_dict[d1].append(d2)
            elif d2 in no_diff_dict:
                no_diff_dict[d2].append(d1)
            else:
                no_diff_dict[d1] = [d2]



    no_diff_str = "\n".join([f"    {', '.join(v)}, and {k}"
                             if len(v)>1 else f"    {k} and {v[0]}"
                             for k, v in no_diff_dict.items()])
    no_diff_str= "There is no difference between:\n" + no_diff_str

    with open(output_file, 'a') as f:
        f.write(f"This is a report on the differences between the different files named {fn}.\n\n")
        if to_write:
            f.write(no_diff_str+"\n\n")
            f.write("\n".join(to_write))
        else:
            f.write(f"Are you sure that you meant to search for {fn}, "
                    f"{'including only ' +filter_list_to_str(only) + ' ' if only else ''}"
                    f"{'excluding ' +filter_list_to_str(excluded) if excluded else ''}?\n"
                    "There are no such files!")

if __name__=="__main__":
    main()