Question

With python 2.7 the following code computes the mD5 hexdigest of the content of a file.

(EDIT: well, not really as answers have shown, I just thought so).

import hashlib

def md5sum(filename):
    f = open(filename, mode='rb')
    d = hashlib.md5()
    for buf in f.read(128):
        d.update(buf)
    return d.hexdigest()

Now if I run that code using python3 it raise a TypeError Exception:

    d.update(buf)
TypeError: object supporting the buffer API required

I figured out that I could make that code run with both python2 and python3 changing it to:

def md5sum(filename):
    f = open(filename, mode='r')
    d = hashlib.md5()
    for buf in f.read(128):
        d.update(buf.encode())
    return d.hexdigest()

Now I still wonder why the original code stopped working. It seems that when opening a file using the binary mode modifier it returns integers instead of strings encoded as bytes (I say that because type(buf) returns int). Is this behavior explained somewhere ?

Answer 1

I think you wanted the for-loop to make successive calls to f.read(128). That can be done using iter() and functools.partial():

import hashlib
from functools import partial

def md5sum(filename):
    with open(filename, mode='rb') as f:
        d = hashlib.md5()
        for buf in iter(partial(f.read, 128), b''):
            d.update(buf)
    return d.hexdigest()

print(md5sum('utils.py'))