hashfiles.py

# This program is valid Python 2.7 and it's also valid Python 3.2.
# To run it, type:  python hashfiles.py
import os, hashlib, collections

# What is a defaultdict? Some sort of data structure, apparently. Hmm.
file_groups = collections.defaultdict(list)

# This loop is going to execute once for each directory in the tree.
for dirpath, dirnames, filenames in os.walk('.'):
    # The inner loop will run once for each file in the tree.
    for f in filenames:
        # Let's just try reading the entire file as one huge string. Why not?
        path = os.path.join(dirpath, f)
        try:
            with open(path, 'rb') as f:
                data = f.read()
        except Exception as exc:
            # Oh dear, some sort of error happpened. Just make a note of it and
            # move on.
            print("skipping: " + path + " because: " + str(exc))
            continue

        # Now take that data and hash it.
        filehash = hashlib.sha256(data).hexdigest()

        # Now file_groups[filehash] is a list. Add path to that list.
        file_groups[filehash].append(path)

# At this point, file_groups contains lots of lists. Each list contains one or
# more files. Now sort each group, so the output is in a nice order.
groups = list(file_groups.values())
for filelist in groups:
    filelist.sort()
groups.sort()

# Print out every group, even groups with just one entry.
for filelist in groups:
    print(filelist[0])
    for f in filelist[1:]:
        print("  = " + f)