I'm writing some mail-processing software in Python that is encountering strange bytes in header fields.  I suspect this is just malformed mail; the message itself claims to be us-ascii, so I don't think there is a true encoding, but I'd like to get out a unicode string approximating the original one without throwing a UnicodeDecodeError.
So, I'm looking for a function that takes a str and optionally some hints and does its darndest to give me back a unicode.  I could write one of course, but if such a function exists its author has probably thought a bit deeper about the best way to go about this.
I also know that Python's design prefers explicit to implicit and that the standard library is designed to avoid implicit magic in decoding text. I just want to explicitly say "go ahead and guess".
The best way to do this that I've found is to iteratively try decoding a prospective with each of the most common encodings inside of a try except block.
Is there a Python library function which attempts to guess the character-encoding of some bytes?