checksum.py

#!/usr/bin/python3
import hashlib, sys

"""
Command line tool to get checksums in python.

Supply filepath for file to process, and which hash
method to use.
"""

def checksum(f, sh='md5', cmp=''):
    ''' Hash file f using method sh. Possible to compare 
    hexdigest with precalculated hash cmp. '''

    try:

        try:
            m = hashlib.new(sh)
        except(ValueError):
            print("Invalid hashing algorithm: {}".format(sh))
            return

        with open(f, 'rb') as infile:
            byte = infile.read(128)
            while byte:
                m.update(byte)
                byte = infile.read(128)

        if cmp:
            # Strip away spaces and make all chars lowercase.
            cmp = cmp.replace(' ','').lower()
            # Compare digest with given precomputed hash to check
            # for a match.
            if(m.hexdigest() == cmp):
                return True
            else:
                return False

        print(m.hexdigest())

    except(FileNotFoundError):
        print("Could not find file: {}".format(f))

if __name__ == '__main__':
    if len(sys.argv) == 2:
        checksum(sys.argv[1])
    elif len(sys.argv) == 3:
        checksum(sys.argv[1], sys.argv[2])
    elif len(sys.argv) == 4:
        checksum(sys.argv[1], sys.argv[2], sys.argv[3])