"""
Implemetation of eiffel like methods (methods with preconditions and postconditions).
eiffelmethod is a new descriptor that implements eiffel like methods. It accepts a method and
optional pre and post conditions. fI the pre or post conditions are not given it searchs methodName_pre
and methodName_post.
"""
import types
class eiffelmethod(object):
def __init__(self, method, pre=None, post = None):
self._method = method
self._pre = pre
self._post = post
def __get__(self, inst, type=None):
result = EiffelMethodWraper(inst,self._method,self._pre, self._post)
setattr(inst, self._method.__name__,result)
return result
class EiffelMethodWraper:
def __init__(self, inst, method, pre, post):
self._inst = inst
self._method = method
if not pre:
pre = getattr(inst,method.__name__+"_pre",None)
if pre: pre = pre.im_func
self._pre = pre
if not post:
post = getattr(inst,method.__name__+"_post",None)
if post: post = post.im_func
self._post = post
def __call__(self, *args, **kargs):
if self._pre:
apply(self._pre,(self._inst,)+args, kargs)
result = apply(self._method,(self._inst,)+args, kargs)
if self._post:
apply(self._post,(self._inst,result)+args, kargs)
return result
def _test():
class C:
def f(self, arg):
return arg+1
def f_pre(self, arg):
assert arg>0
def f_post(self, result, arg):
assert result>arg
f = eiffelmethod(f,f_pre,f_post)
c = C()
c.f(1)
try:
c.f(-1)
except AssertionError:
pass
else:
raise "c.f(-1) bad implemented"
print "OK"
if __name__=='__main__':
_test()
