pmatching.py

# coding: utf8


"""Simple pattern matching function dispatch through a decorator

Example:

@matchs(int)
def myfunc(i):
    print "int received:", i

@matchs(str):
def myfunc(s):
    print "str received:", s

myfunc(1)
myfunc("s")
   
"""


class PatternMatchingError(Exception):
    "Raised when there is not matching pattern"

    
class PatternHandler(object):
    "Function cache and dispatcher"
    
    cache = {}
    
    def __init__(self, f, *args, **kwargs):
        "Store the function and its signature in the cache"
        kwargs_tuple = tuple(kwargs.items())
        fname = self.__name__ = f.__name__
        self.cache[(fname, args, kwargs_tuple)] = f

    def __call__(self, *args, **kwargs):
        "Dispatch to the proper function"
        args_t = tuple(type(t) for t in args)
        kwargs_t = tuple((name, type(t)) for name, t in kwargs.items())
        fname = self.__name__
        func = self.cache.get((fname, args_t, kwargs_t), None)
        if not func:
            raise PatternMatchingError("Function not found")
        return func(*args, **kwargs)


def matchs(*args, **kwargs):
    "Declare that a function handles a pattern"
    def decorator(f):
        return PatternHandler(f, *args, **kwargs)
    return decorator