On Mon, 24 Oct 2011 16:29:25 -0500, Andrew Berg wrote:
> I want to create a decorator with two different (but very similar)
> versions of the wrapper function, but without copying giant chunks of
> similar code. The main difference is that one version takes extra
> parameters.
>
> def test_dec(func, extra=False):
> if extra:
> def wrapper(ex_param1, ex_param2, *args, **kwargs):
> print('bla bla')
> print('more bla')
> print(ex_param1)
> print(ex_param2)
> func(ex_param1, ex_param2, *args, **kwargs)
> else:
> def wrapper(*args, **kwargs):
> print('bla bla')
> print('more bla')
> func(*args, **kwargs)
> return wrapper
>
> If the function I'm wrapping takes ex_param1 and ex_param2 as
> parameters, then the decorator should print them and then execute the
> function, otherwise just execute the function. I'd rather not write
> separate wrappers that are mostly the same.
In principle you could inspect the function's calling signature using the
inspect module, and then decide how to decorate it from that. But I
recommend against that: it's too much like magic.
This is how I would do it:
from functools import wraps
def decorator_factory(extras=None):
"""Factory function which returns a decorator.
Usage:
@decorator_factory(): # Note you need the parentheses.
def spam(...):
return ...
@decorator_factory((extra1, extra2)):
def spam(...):
return ...
"""
# Inner function performing common functionality.
def preamble():
print('bla bla')
print('more bla')
# Decide what sort of decorator is needed.
if extras is None:
# Create decorator style 1.
def decorator(func):
@wraps(func)
def inner(*args, **kwargs):
preamble()
return func(*args, **kwargs)
return inner
else:
# Create decorator style 2.
extra1, extra2 = extras
def decorator(func):
@wraps(func)
def inner(*args, **kwargs):
preamble()
print(extra1)
print(extra2)
return func(extra1, extra2, *args, **kwargs)
return inner
return decorator
If you don't like nested functions inside nested functions, you can pull
out the inner functions:
def preamble():
print('bla bla')
print('more bla')
def plain_decorator(func):
@wraps(func)
def inner(*args, **kwargs):
preamble()
return func(*args, **kwargs)
return inner
def extra_decorator(func):
@wraps(extra1, extra2, func)
def inner(*args, **kwargs):
preamble()
print(extra1)
print(extra2)
return func(extra1, extra2, *args, **kwargs)
return inner
def decorator_factory(plain):
if plain:
return plain_decorator
else:
return extra_decorator
--
Steven
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