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# coding: utf-8
import warnings
import deprecated.classic
def with_metaclass(meta, *bases):
"""Create a base class with a metaclass."""
# This requires a bit of explanation: the basic idea is to make a dummy
# metaclass for one level of class instantiation that replaces itself with
# the actual metaclass.
class metaclass(type):
def __new__(cls, name, this_bases, d):
return meta(name, bases, d)
@classmethod
def __prepare__(cls, name, this_bases):
return meta.__prepare__(name, bases)
return type.__new__(metaclass, 'temporary_class', (), {})
def test_with_init():
@deprecated.classic.deprecated
class MyClass(object):
def __init__(self, a, b=5):
self.a = a
self.b = b
with warnings.catch_warnings(record=True) as warns:
warnings.simplefilter("always")
obj = MyClass("five")
assert len(warns) == 1
assert obj.a == "five"
assert obj.b == 5
def test_with_new():
@deprecated.classic.deprecated
class MyClass(object):
def __new__(cls, a, b=5):
obj = super(MyClass, cls).__new__(cls)
obj.c = 3.14
return obj
def __init__(self, a, b=5):
self.a = a
self.b = b
with warnings.catch_warnings(record=True) as warns:
warnings.simplefilter("always")
obj = MyClass("five")
assert len(warns) == 1
assert obj.a == "five"
assert obj.b == 5
assert obj.c == 3.14
def test_with_metaclass():
class Meta(type):
def __call__(cls, *args, **kwargs):
obj = super(Meta, cls).__call__(*args, **kwargs)
obj.c = 3.14
return obj
@deprecated.classic.deprecated
class MyClass(with_metaclass(Meta)):
def __init__(self, a, b=5):
self.a = a
self.b = b
with warnings.catch_warnings(record=True) as warns:
warnings.simplefilter("always")
obj = MyClass("five")
assert len(warns) == 1
assert obj.a == "five"
assert obj.b == 5
assert obj.c == 3.14
def test_with_singleton_metaclass():
class Singleton(type):
_instances = {}
def __call__(cls, *args, **kwargs):
if cls not in cls._instances:
cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
return cls._instances[cls]
@deprecated.classic.deprecated
class MyClass(with_metaclass(Singleton)):
def __init__(self, a, b=5):
self.a = a
self.b = b
with warnings.catch_warnings(record=True) as warns:
warnings.simplefilter("always")
obj1 = MyClass("five")
obj2 = MyClass("six", b=6)
# __new__ is called only once:
# the instance is constructed only once,
# so we have only one warning.
assert len(warns) == 1
assert obj1.a == "five"
assert obj1.b == 5
assert obj2 is obj1
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