"""This module contains code from
Think Python by Allen B. Downey

http://thinkpython.com

Copyright 2012 Allen B. Downey
License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html

"""

import os

def walk(dirname):
??? """Finds the names of all files in dirname and its subdirectories.

??? dirname: string name of directory
??? """
??? names = []
??? for name in os.listdir(dirname):
??????? path = os.path.join(dirname, name)

??????? if os.path.isfile(path):
??????????? names.append(path)
??????? else:
??????????? names.extend(walk(path))
??? return names

def compute_checksum(filename):
??? """Computes the MD5 checksum of the contents of a file.

??? filename: string
??? """
??? cmd = 'md5sum ' + filename
??? return pipe(cmd)

def check_diff(name1, name2):
??? """Computes the difference between the contents of two files.

??? name1, name2: string filenames
??? """
??? cmd = 'diff %s %s' % (name1, name2)
??? return pipe(cmd)

def pipe(cmd):
??? """Runs a command in a subprocess.

??? cmd: string Unix command

??? Returns (res, stat), the output of the subprocess and the exit status.
??? """
??? fp = os.popen(cmd)
??? res = fp.read()
??? stat = fp.close()
??? assert stat is None
??? return res, stat

def compute_checksums(dirname, suffix):
??? """Computes checksums for all files with the given suffix.

??? dirname: string name of directory to search
??? suffix: string suffix to match

??? Returns: map from checksum to list of files with that checksum
??? """
??? names = walk(dirname)

??? d = {}
??? for name in names:
??????? if name.endswith(suffix):
??????????? res, stat = compute_checksum(name)
??????????? checksum, _ = res.split()

??????????? if checksum in d:
??????????????? d[checksum].append(name)
??????????? else:
??????????????? d[checksum] = [name]

??? return d

def check_pairs(names):
??? """Checks whether any in a list of files differs from the others.

??? names: list of string filenames
??? """
??? for name1 in names:
??????? for name2 in names:
??????????? if name1 < name2:
??????????????? res, stat = check_diff(name1, name2)
??????????????? if res:
??????????????????? return False
??? return True

def print_duplicates(d):
??? """Checks for duplicate files.

??? Reports any files with the same checksum and checks whether they
??? are, in fact, identical.

??? d: map from checksum to list of files with that checksum
??? """
??? for key, names in d.iteritems():
??????? if len(names) > 1:
??????????? print 'The following files have the same checksum:'
??????????? for name in names:
??????????????? print name

??????????? if check_pairs(names):
??????????????? print 'And they are identical.'

if __name__ == '__main__':
??? d = compute_checksums(dirname='.', suffix='.py')
??? print_duplicates(d)