String Comparisons returning score

[Clayton Brown - Emmie Osawa]

Is there an approved standard library/function/algarithm for comparing
two similar strings and returning a percentage match?

I am aware of soundEx.py / .c  which is based on the grammar and
phonetics of words, but from what I have read it seems to be flawed..
and thus removed from the python standard library.

I have noticed similar techniques in other languages which are based
on shift matrixes, working out the minimum number of changes to
transform string A into string B.

I am more looking for one which looks at 
words/
chars/
char-order/
length/
similarity
perhaps omitting spaces, and a common library (the,a,and,mr,mrs......)
with a weighted scoring mechanism...

Thanks in advance...
Clayton Brown / Emmie Osawa