Accessing self within decorator function within a Python class

Question

I've got a decorator function I'm applying to functions within a class. The decorator is supposed to do a check against an _api member variable. However, I get a global name 'self' is not defined error when I try to do this. What's the right way?

def requires_api(fn):
    def wrapped(*args, **kwargs):
        if self._api is not None:
            return fn(*args, **kwargs)
        else:
            return None
    return wrapped


@requires_api       
def do_something(self):
...

kindall · Accepted Answer · 2012-04-08T16:26:03.180

5

The reference to your instance is in your wrapper function's *args so the name self isn't avaialble. Use args[0], or just rewrite it as:

def wrapper(self, *args, **kwargs):
    # ...

Naturally, if you do this, your call through to the wrapped function should also include self.

edited Apr 08 '12 at 16:26

answered Apr 08 '12 at 16:13

kindall

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score 1 · Answer 2 · edited Apr 08 '12 at 16:30

1

Change

if self._api is not None:

to

if hasattr(args[0], '_api'):

args[0] has self. hasattr is the right way to check for an attribute.

If you try to access an attribute that does not exist, (if self._api does not exist) you will generate an AttributeError.

edited Apr 08 '12 at 16:30

Joel Cornett

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answered Apr 08 '12 at 16:19

Steven Rumbalski

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1

Thanks, you're correct, that was a mis-statement on my part- should be a comment though – Yarin Apr 08 '12 at 16:26
@Yarin: What should be a comment? – Steven Rumbalski Apr 08 '12 at 16:29
@JoelCornett: Thanks for the edit. Found it just as I was preparing to write the same thing. :) – Steven Rumbalski Apr 08 '12 at 16:31
@StevenRumbalski: No problem. That's usually how it happens :) – Joel Cornett Apr 08 '12 at 16:32

Accessing self within decorator function within a Python class

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