Testing a Collatz Conjecture Conjecture (Python)
def key(value, dct):
    for key in dct.keys():
        if dct[key] == value:
            return key
    return None



This is really inefficient and not how dictionaries should be used.


The point of a dict is O(1) lookup, this is essentially O(n) and it doesn't make sense
You should remove your blockcomments, and create a nice docstring. That will make the purpose of the code clearer
You don't close the file, a nice addition is using the with statement to automatically open/close files PEP343