Hashing with hashlib with user interaction

Question

I am trying to create a hashing function with user interaction. The idea is that the user chooses which hash he/she wants (i.e. md5, sha1 and so forth) and the program does the rest.

My code:

hashstring = "hashlib" + finalHash

    filePath = open(chosenFile, 'rb')

    data = filePath.read(8192)

    if not data:
        return

    hashstring.update(data) # The line that causes error

    return hashstring.hexdigest()

finalHash is from a dictionary containing (lets say md5 is chosen) '.md5()' so the string from hashstring is 'hashlib.md5().

I get the error: AttributeError: 'str' object has no attribute 'update', the error points me to the obvious: hashstring is a string (as i declared it), my question goes: How do i convert or in other way make it useable as it is intended?

Answer 1

You could use getattr:

import hashlib
chosenFile = '/etc/passwd'
finalHash = input('Which hash function?') # raw_input in Python 2
assert finalHash in ['md5', 'sha1'] # Optional
h = getattr(hashlib, finalHash)
h.update(open(chosenFile, 'rb').read())
print(h.hexdigest())

Note that the input must not contain dots or parentheses. If you want to allow the user to input md5() or so, you'll have to strip the parentheses first.