Copy unique files from multiple folders into a new folder

diff-folders.py

#!/usr/bin/env python
#-*- coding: utf-8 -*-

"""
Merge two folders together using a diff digest program
If a folders have multiple files of the same digest, 
ignore the duplicates and proceed to copy the unique files 
into a new target folder. If the folder doesn't exist, 
create a new one.

This does not preserve file name as files may have 
overlapping names and thus cannot be preserved
"""

import shutil
import os
import os.path
from sys import argv
from subprocess import getstatusoutput

call = lambda p: getstatusoutput(p)[1]
sham = "sha256sum"

def diff_folders(new_folder, *folders):
    """
    Diff N folders with possibly the same files
    Apply sha256sum to each file and obtain it's sha256 digest
    Use a digest => file_path dictionary
    If a digest exists, possible file duplicate
    Afterwards, copy all unique files to a new folder
    """
    if not os.path.isdir(new_folder):
        os.mkdir(new_folder)
    digests = {}
    for folder in folders:
        d_added = 0
        files = [os.path.join(folder, f) for f in os.listdir(folder)]
        print("There are {} files in {}".format(len(files), folder))
        for f in files:
            sha = call("{} {}".format(sham, f)).split(" ")[0]
            print(sha)
            if sha not in digests:
                digests[sha] = f
                d_added += 1
        print("{} digests were added".format(d_added))

    print("There are {} pairs in the digest dict".format(len(digests)))
    for i, f in enumerate(digests.values()):
        print("Copying {} to new folder...".format(f))
        s = "{}"
        if "." in f:
            s = s.format("{}."+f.split(".")[-1])
        shutil.copy(f, os.path.join(new_folder, s.format(i)))
    print("done")
        
if __name__ == "__main__":
    diff_folders(argv[1], *argv[2:])