python: why use a wrapper in decorator?

Question

def synchronized(func):
    """Decorator for storage-access methods, which synchronizes on a threading
    lock. The parent object must have 'is_closed' and '_sync_lock' attributes.
    """

    @wraps(func)
    def synchronized_wrapper(self, *args, **kwargs):
        with self._sync_lock:
           return func(self, *args, **kwargs)

    return synchronized_wrapper

the code is in whoosh/src/util.py,I can't understand the synchronized_wrapper's effect and the parameters in synchronized_wrapper(self, *args, **kwargs) from where. Can anyone give me some pointers?

http://stackoverflow.com/questions/308999/what-does-functools-wraps-do — lucemia, Dec 12 '12 at 02:57

score 0 · Accepted Answer · answered Dec 12 '12 at 02:57

The @wraps decorator is just syntactic sugar for a function closure with argument forwarding. *args refers to a tuple of positional args, and **kwargs refers to a dict of all keyword args that have been passed to func.

Hence if you had:

def f(foo, bar=None):
    ...

and did:

sync_f = someinst.synchronized(f)
sync_f(a, bar=z)

it would basically be like calling:

f(a, bar=z)

but inside the "with self._sync_lock:" context manager

score 0 · Answer 2 · edited May 23 '17 at 12:29

0

Decorating a function causes problems with reflection-based operations, and @wraps is designed to make the wrapped function truly simulate the original function. The link lucemia provided has applicable info.

edited May 23 '17 at 12:29

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answered Dec 12 '12 at 03:06

acjay

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python: why use a wrapper in decorator?

2 Answers2