Exercise 10.4

Objectives:

Learning about Decorators

Files Created: timethis.py

Files Modified: None

If you define a function, its name and module are stored in the __name__ and __module__ attributes. For example:

>>> def add(x,y):
     return x+y

>>> add.__name__
'add'
>>> add.__module__
'__main__'
>>>

In a file timethis.py, write a decorator function timethis(_func_) that wraps a function with an extra layer of logic that prints out how long it takes for a function to execute. To do this, you’ll surround the function with timing calls like this:

start = time.time()
r = func(*args,**kwargs)
end = time.time()
print '%s.%s: %f' % (func.__module__, func.__name__, end-start)

Here is an example of how your decorator should work:

>>> from timethis import timethis
>>> @timethis
    def countdown(n):
        while n > 0:
             n -= 1

>>> countdown(10000000)
__main__.countdown : 0.076562
>>>

Discussion: This @timethis decorator can be placed in front of any function definition. Thus, you might use it as a diagnostic tool for performance tuning.

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