A4 portrait - PET: Python Entre Todos - Python Argentina

Ingredients 28
In this article i’m going to write about how to code decorators in our favourite
language.
A decorator is basically a callable 1 that wraps another and which allows us to modify
the behavior of the wrapped one. This might sound complicated at the beginning but
it is really easier than it seems.
Now, without any further ado we are going to cook some tasty home-baked wrapped
callables.
Ingredients
• a callable
• a decorator
• coffee (optional)
• sugar (opcional)
Our to-be-wrapped callable for example will look like this:
def yes(string='y', end='\n'):
"""outputs `string`.
This is similar to what the unix command `yes` does.
Default value for `string` is 'y'
"""
print(string, sep='', end=end)
Our decorator used to wrap the callable looks like this:
def log_callable(callable):
"""Decorates callable and logs information about it.
Logs how many times the callable was called and the params it had.
"""
if not getattr(log_callable, 'count_dict', None):
log_callable.count_dict = {}
log_callable.count_dict.setdefault(
callable.__name__, 0
)
def wrap(*args, **kwargs):
callable(*args, **kwargs)
log_callable.count_dict[callable.__name__] += 1
message = []
message.append(
"""called: '{0}' '{1} times'""".format(
callable.__name__,
log_callable.count_dict[callable.__name__]
)
)
message.append(
"""Arguments: {0}""".format(
", ".join(map(str, args))
)
PET: English Translation (Issue 1, August 2010) — http://revista.python.org.ar