两个小例子彻底明白python decorator

一：没有什么实际意思，就是单纯的理解decorator。使用装饰器完全可以阻止方法中的代码执行。

class json_test(object):
  def __init__(self, *arg, **args):
    self.name = 'default_name'
    self.gender = 'default_gender'
    self.age = 0
    self.address = None
jt = json_test()

class ignore_null_value(object):
  def __init__(self, *args, **kwargs):
    print('ignore_null_value.init')
    
  @staticmethod
  def to_json(*arg, **args):
    d = {}
    for key, value in arg[0].__dict__.items():
      if value != None:
        d.setdefault(key, value)
    for key, value in args:
      d.setdefault(key, value)
    return d
    
    
class keep_null_value(object):
  def __init__(self, *args, **kwargs):
    print('keep_null_value.init')
    
  @staticmethod
  def to_json(o):
    return o.__dict__

def deco(c):
  def _deco(func):
    def __deco(*arg, **args):
      print('before')
      try:
        s = c.to_json(*arg, **args)
        return s 
      finally:
        print('after')
    return __deco
  return _deco

class c(object):
  @staticmethod
  @deco(keep_null_value)
  def json_from(self, a):
    pass

cl = c()
print cl.json_from(jt)

二：输出前后加上log，这个是书中的原例子，哪本书不记得了，不是《python基础教程》就是《python核心编程》

from time import time

def logged(when):
  def log(f, *args, **kargs):
      print '''Called:
  function: %s
  args: %r
  kargs: %r''' % (f, args, kargs)

  def pre_logged(f):
    def wrapper(*args, **kargs):
      log(f, *args, **kargs)
      return f(*args, **kargs)
    return wrapper

  def post_logged(f):
    def wrapper(*args, **kargs):
      now = time()
      try:
        log(f, *args, **kargs)
        return f(*args, **kargs)
      finally:
        print "time delta: %s" % (time() - now)
    return wrapper
  try:
    return {"pre": pre_logged, "post": post_logged}[when]
  except KeyError, e:
    raise ValueError(e), 'must be "pre" or "post"'
                    
@logged("post")
def hello(name):
    print "Hello,", name
    
hello("World!")