Python: Hash function always produces same (empty) hash for any file-CodePudding

So I did a ton of googling around but can't really find an answer to my problem. I tried to make a function to hash bigger files, and I made two different functions, yet both seem to produce the same output for any file I hash, to be precise:

e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

which I know is the SHA256 hash of an empty bite string.

The two solutions I tried to use were:

from hashlib import sha256 as hashfun

bs = 1048576                   # I'll just use 1024kb chunks as an example
selectfile = "/PATH/TO/FILE"

with open(selectfile, 'rb') as f:
    for chunk in iter(lambda: f.read(bs), b''):
        hashfun().update(chunk)
    print(hashfun().hexdigest())

and

from hashlib import sha256 as hashfun

bs = 1048576
selectfile = "/PATH/TO/FILE"

with open(selectfile, 'rb') as f:
    while True:
        data = f.read(bs)
        if not data:
            break
        hashfun().update(data)
    print(hashfun().hexdigest())

Neither of these seems to function. I know that the file is not the issue since a simple function without the block reading worked before:

from hashlib import sha256 as hashfun

selectfile = "/PATH/TO/FILE"

with open(selectfile, 'rb') as f:
    rbytes = f.read()
    readable_hash = hashfun(rbytes).hexdigest()
    print(readable_hash)

Is there something super obvious that I am doing wrong here (probably lol)? Thanks in advance!

CodePudding user response：

The code is calling the hash constructor repeatedly instead of creating a single hash instance and updating it.

This should work:

from hashlib import sha256 as hashfun

bs = 1048576                   # I'll just use 1024kb chunks as an example
selectfile = "/PATH/TO/FILE"
hash_ = hashfun()

with open(selectfile, 'rb') as f:
    for chunk in iter(lambda: f.read(bs), b''):
        hash_.update(chunk)
    print(hash_.hexdigest())