python2与python3中__metacalss__的不同用法

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