python decorator simple example

Why we need the decorator in python ?

Let's see a example:

#!/usr/bin/python

def fun_1(x):
    return x*2 

def fun_2(x):
    return x*x*2

if __name__ == '__main__':
    print 'call fun_1'
    print fun_1(8)
    print 'call fun_2'
    print fun_2(9)

We can see more than code heavy:

so we don't want to write the below code any more ...

print 'call fun_1'
print 'call fun_2'

How can we do it with a simple way !

Try use decorator:

#!/usr/bin/python

def fun_decorator(f):
    def fn(x):
        print 'call '+f.__name__
        return f(x)
    return fn

@fun_decorator
def fun_1(x):
    return x*2 
@fun_decorator
def fun_2(x):
    return x*x*2

if __name__ == '__main__':
    print fun_1(8)
    print fun_2(9)

See the result below:

But,sometime We are expect to write something before or after tips:

something like below,we add some at the head ..

How to make it ?

a simple and stupid method below:

#!/usr/bin/python

def fun_decorator(f):
    def fn(x):
        print 'call '+f.__name__
        return f(x)
    return fn

@fun_decorator
def fun_1(x):
    return x*2 
@fun_decorator
def fun_2(x):
    return x*x*2

if __name__ == '__main__':
    print 'INFO',fun_1(8)
    print 'DEBUG',fun_2(9)

You can see,we are just simply add some string before call function !

So,How to make it easy ..

#!/usr/bin/python

def fun_decorator(user_info):
    def wrapper(f):
        def fn(x):
            print '%s call %s' % (user_info,f.__name__)
            return f(x)
        return fn
    return wrapper

@fun_decorator('INFO')
def fun_1(x):
    return x*2 
@fun_decorator('DEBUG')
def fun_2(x):
    return x*x*2

if __name__ == '__main__':
    print fun_1(8)
    print fun_2(9)

If you function with more than one argument,How can we do ?

#!/usr/bin/python

def fun_decorator(user_info):
    def wrapper(f):
        def fn(x,y):
            print '%s call %s' % (user_info,f.__name__)
            return f(x,y)
        return fn
    return wrapper


@fun_decorator("INFO")    
def fun_1(x,y):
    return x*y 

@fun_decorator("INFO")
def fun_2(x,y):
    return x*y*2

if __name__ == '__main__':

    print fun_1(2,3)
    print fun_2(2,3)

Okay,Sometime,we even don't know how many arguments will be input ?

so,How can we do ?

>>>we will answer it next time ! Thank you