python2与python3中__metacalss__的不同用法
Posted 思辨
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python3
def upper_attr(future_class_name, future_class_parents, future_class_attr): attrs = ((name, value) for name, value in future_class_attr.items() if not name.startswith(‘__‘)) uppercase_attr = dict((name.upper(), value) for name, value in attrs) return type(future_class_name, future_class_parents, uppercase_attr) class Foo(metaclass = upper_attr): bar = ‘bip‘ print(hasattr(Foo, ‘bar‘)) print(hasattr(Foo, ‘BAR‘)) f = Foo() print(hasattr(f,‘bar‘)) print(hasattr(f,‘BAR‘))
输出:
False
True
False
True
Process finished with exit code 0
python2:
def upper_attr(futer_class_name, future_class_parent, futuer_class_attr):
attrs = ((name, value) for name, value in futuer_class_attr.item() if name.startswith(‘__‘))
uppercase_attr = dict((name.upper(),value) for name, value in attrs)
return type(futer_class_name, future_class_parent, uppercase_attr)
__metaclass__ = upper_attr
class Foo(object):
bar = ‘bip‘
print(hasattr(Foo, ‘bar‘))
print(hasattr(Foo, ‘BAR‘))
f = Foo()
print(hasattr(f,‘bar‘))
print(hasattr(f,‘BAR‘))
关于Python2对__metaclass__的跟详细的解释请看:
http://blog.jobbole.com/21351/ -------------python2中__metaclass__的用法
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