装饰器在全局变量中不起作用

Question

I set attribute for func by a decorator function, but can not get it in globals()

here is the code

def tag(name):
    def do_it(func):
        func.tag = name
        return func
    return do_it


@tag('p')
def article():
    return 'article here'


@tag('h1')
def title():
    return 'title here'

# we got attribute here
assert hasattr(article, 'tag', None)

# I got nothing here
for obj in list(globals()):
    if hasattr(obj, 'tag'):
        print(obj)

anybody know why ?

Answer 1

The problem lies with your use of globals() ; it returns a dictionary, and calling list() on a dictionary gives you the keys , not the objects. You are testing against strings here.

Use:

for name, obj in list(globals().items()):
    if hasattr(obj, 'tag'):
        print name

The list() is still needed as the code adds 2 extra globals ( name and obj ), so the globals() dictionary changes size in the first iteration, something that'll throw an exception otherwise.

Your decorator is working fine otherwise.

Answer 2

Indeed it is in globals.

def tag(name):
    def do_it(func):
        func.tag = name
        return func
    return do_it

@tag('p')
def article():
    return 'article here'

'tag' in globals()
True

The point is when iterate over globals (even in na list), it will be a string representation of item of globals.

So should try this way

for obj in globals():
    if obj == 'tag':
        print(obj)

Anyway every object will appear as a string. This only will asserts that this object is in globals.

I recommend you to read about scoping and namesapecing. This is a good article about it.