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In [1]:

    
def add(a,b):
    return a+b



In [2]:

    
add(3,4)









    Out[2]:





7

What if we want to log when that function is called?



In [3]:

    
def logged_add(a, b):
    print '### %s(%r, %r)' % ('add', a, b)
    result = add(a, b)
    print '### %s(%r, %r) --> %r' % ('add', a, b, result)
    return result

could change all calls to this -- blech!

so instead write a wrapper:



In [5]:

    
def logged(func):
    def wrapper(a, b):
        print '### %s(%r, %r)' % (func.func_name, a, b)
        result = func(a, b)
        print '### %s(%r, %r) --> %r' % (func.func_name, a, b, result)
        return result
    return wrapper

re-define add...



In [6]:

    
add = logged(add)



In [6]:

    
add(3,4)









    



### add(3, 4)
### add(3, 4) --> 7






    Out[6]:





7

And use it for other functions, too:



In [7]:

    
def subtract(a, b):
    """subtract() subtracts two things"""
    return a - b
subtract = logged(subtract)



In [8]:

    
subtract(7,4)









    



### subtract(7, 4)
### subtract(7, 4) --> 3






    Out[8]:





3

Make it more general -- to take any number of arguments:



In [9]:

    
def logged(func):
    def wrapper(*args):
        print '### %s(%s)' % (func.func_name, args)
        result = func(*args)
        print '### %s(%s) --> %r' % (func.func_name, args, result)
        return result
    return wrapper

A function with one argument:



In [10]:

    
def even(a):
    """even() returns True if the value is even"""
    return a % 2 == 0
even = logged(even)



In [11]:

    
even(3)









    



### even((3,))
### even((3,)) --> False






    Out[11]:





False



In [12]:

    
even(4)









    



### even((4,))
### even((4,)) --> True






    Out[12]:





True



In [12]:



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