really stupid plural checker.

plurals.py

def is_plural(a,b):
    """a really stupid pluralisation checker, english only
    returns true if b is standard form plural of a (or vis-a-versa) as defined by these rules:
        adds s or es
        subs y for ies
        subs f or fe for ves
    based on http://en.wikipedia.org/wiki/English_plural this should cover regular and near-regular plurals
    """
    if len(a) == len(b):
        #all [near-]regular plurals are longer, so:
        return False
    singular = min(a,b,key=len).lower()
    plural = max(a,b,key=len).lower()
    
    if singular + 's' == plural or singular + 'es' == plural:
        return True
    
    if singular[-1] == 'y':
        if singular[:-1] + 'ies' == plural:
            return True
            
    if singular[-1] == 'f' or singular[-2:] == 'fe':
        if singular[:-1] + 'ves' == plural or singular[:-2] + 'ves' == plural:
            return True
    
    #fail
    return False