mirror of
https://github.com/python/cpython.git
synced 2025-11-04 03:44:55 +00:00
146 lines
3.8 KiB
Python
Executable file
146 lines
3.8 KiB
Python
Executable file
#!/usr/bin/env python3
|
|
|
|
"""
|
|
Support Eiffel-style preconditions and postconditions for functions.
|
|
|
|
An example for Python metaclasses.
|
|
"""
|
|
|
|
import unittest
|
|
from types import FunctionType as function
|
|
|
|
class EiffelBaseMetaClass(type):
|
|
|
|
def __new__(meta, name, bases, dict):
|
|
meta.convert_methods(dict)
|
|
return super(EiffelBaseMetaClass, meta).__new__(
|
|
meta, name, bases, dict)
|
|
|
|
@classmethod
|
|
def convert_methods(cls, dict):
|
|
"""Replace functions in dict with EiffelMethod wrappers.
|
|
|
|
The dict is modified in place.
|
|
|
|
If a method ends in _pre or _post, it is removed from the dict
|
|
regardless of whether there is a corresponding method.
|
|
"""
|
|
# find methods with pre or post conditions
|
|
methods = []
|
|
for k, v in dict.items():
|
|
if k.endswith('_pre') or k.endswith('_post'):
|
|
assert isinstance(v, function)
|
|
elif isinstance(v, function):
|
|
methods.append(k)
|
|
for m in methods:
|
|
pre = dict.get("%s_pre" % m)
|
|
post = dict.get("%s_post" % m)
|
|
if pre or post:
|
|
dict[k] = cls.make_eiffel_method(dict[m], pre, post)
|
|
|
|
|
|
class EiffelMetaClass1(EiffelBaseMetaClass):
|
|
# an implementation of the "eiffel" meta class that uses nested functions
|
|
|
|
@staticmethod
|
|
def make_eiffel_method(func, pre, post):
|
|
def method(self, *args, **kwargs):
|
|
if pre:
|
|
pre(self, *args, **kwargs)
|
|
rv = func(self, *args, **kwargs)
|
|
if post:
|
|
post(self, rv, *args, **kwargs)
|
|
return rv
|
|
|
|
if func.__doc__:
|
|
method.__doc__ = func.__doc__
|
|
|
|
return method
|
|
|
|
|
|
class EiffelMethodWrapper:
|
|
|
|
def __init__(self, inst, descr):
|
|
self._inst = inst
|
|
self._descr = descr
|
|
|
|
def __call__(self, *args, **kwargs):
|
|
return self._descr.callmethod(self._inst, args, kwargs)
|
|
|
|
|
|
class EiffelDescriptor:
|
|
|
|
def __init__(self, func, pre, post):
|
|
self._func = func
|
|
self._pre = pre
|
|
self._post = post
|
|
|
|
self.__name__ = func.__name__
|
|
self.__doc__ = func.__doc__
|
|
|
|
def __get__(self, obj, cls):
|
|
return EiffelMethodWrapper(obj, self)
|
|
|
|
def callmethod(self, inst, args, kwargs):
|
|
if self._pre:
|
|
self._pre(inst, *args, **kwargs)
|
|
x = self._func(inst, *args, **kwargs)
|
|
if self._post:
|
|
self._post(inst, x, *args, **kwargs)
|
|
return x
|
|
|
|
|
|
class EiffelMetaClass2(EiffelBaseMetaClass):
|
|
# an implementation of the "eiffel" meta class that uses descriptors
|
|
|
|
make_eiffel_method = EiffelDescriptor
|
|
|
|
|
|
class Tests(unittest.TestCase):
|
|
|
|
def testEiffelMetaClass1(self):
|
|
self._test(EiffelMetaClass1)
|
|
|
|
def testEiffelMetaClass2(self):
|
|
self._test(EiffelMetaClass2)
|
|
|
|
def _test(self, metaclass):
|
|
class Eiffel(metaclass=metaclass):
|
|
pass
|
|
|
|
class Test(Eiffel):
|
|
def m(self, arg):
|
|
"""Make it a little larger"""
|
|
return arg + 1
|
|
|
|
def m2(self, arg):
|
|
"""Make it a little larger"""
|
|
return arg + 1
|
|
|
|
def m2_pre(self, arg):
|
|
assert arg > 0
|
|
|
|
def m2_post(self, result, arg):
|
|
assert result > arg
|
|
|
|
class Sub(Test):
|
|
def m2(self, arg):
|
|
return arg**2
|
|
|
|
def m2_post(self, Result, arg):
|
|
super(Sub, self).m2_post(Result, arg)
|
|
assert Result < 100
|
|
|
|
t = Test()
|
|
self.assertEqual(t.m(1), 2)
|
|
self.assertEqual(t.m2(1), 2)
|
|
self.assertRaises(AssertionError, t.m2, 0)
|
|
|
|
s = Sub()
|
|
self.assertRaises(AssertionError, s.m2, 1)
|
|
self.assertRaises(AssertionError, s.m2, 10)
|
|
self.assertEqual(s.m2(5), 25)
|
|
|
|
|
|
if __name__ == "__main__":
|
|
unittest.main()
|