python-decorators(http://xahlee.info/perl-python/python_decorator.html)

decorate.py

#/usr/bin/env python

# ex1.py      

@g
def f():
    print("xyz")

# is equivalent to                                                                                                                                    
def f():
    print("xyz")
f = g(f)

# -----

# ex2.py
# Example of decorator

def gg(xx):
    print "gg called"
    def s(y):
        return y-1
    return s


@gg
def ff(x):
    print "ff called"
    return x+1


print ff(3)

# -----

# ex3.py
# Check/Modify input argument

def gg(func):
    """A decorator for ff. Make sure input to ff is always even, else, add
    1 to make it even."""

    def hh(y):
        if y % 2 ==0:
            return func(y)
        else:
            return func(y+1)
    return hh


@gg
def ff(x):
    return x

print ff(3)
print ff(2)
print ff(9)

# -----

# ex4.py
# Example of decorator that check condition to decide whether to call

cc = True                       # change this to False to toggle
                                # decorator action.

def gg(func):                   # decorator
    """a decorator for ff. If cc is true, run ff, else do nothing."""
    def hh(*args, **kwargs):    # params must catch all args of ff
        """do nothing function"""
        pass
    if cc:
        return func
    else:
        return hh


@gg
def ff(*args, **kwargs):
    # ff can be sending email, or any callable with no return value
    print "ff"
    pass


ff()    
ff(3)
ff(3, "jane")
ff(3,4,k="thankyou")

# -----

# ex5.py
# Decorator with parameter

'''
@g(3)
def f():
    print("xyz")

is equivaqlent to

def f():
    print("xyz")

f = g(3)(f)

'''

def gg(num):
    """a decorator for ff. Ignore ff. Simply return num."""
    def h1(f1):
        def h2(f2):
            return num
        return h2
    return h1

# gg(1) must return a function h1, such that h1 accept function (the
# ff), and also return a function (to be applied to ff's args))

@gg(1)
def ff(x):
    return repr(x) + " rabbits"

print ff(3)
print ff(4)