详解python中的闭包

def make_printer(msg):
  def printer():
    print(msg) # 夹带私货（外部变量）
 
  return printer # 返回的是函数，带私货的函数
 
 
printer = make_printer("Foo!")
printer()

def tag(tag_name):
  def add_tag(content):
    return "<{0}>{1}</{0}>".format(tag_name, content)
  return add_tag
 
content = "Hello"
 
add_tag = tag('a')
print(add_tag(content)) # <a>Hello</a>
 
add_tag = tag('b')
print(add_tag(content)) # <b>Hello</b>

# how to define
def wrapper(func1): # 接受一个callable对象
  return func1 # 返回一个对象，一般为函数
 
 
# how to use
def target_func(args): # 目标函数
  pass
 
 
# 调用方式1，直接包裹
result = wrapper(target_func("123"))
 
# 调用方式2，使用@语法，等同于方式1
@wrapper
def target_func(args):
  pass
 
result = target_func()

def html_tags(tag_name):
  def wrapper_(func):
    def wrapper(*args, **kwargs):
      content = func(*args, **kwargs)
      return "<{tag}>{content}</{tag}>".format(tag=tag_name, content=content)
    return wrapper
  return wrapper_
 
 
@html_tags('a')
def hello(name='Toby'):
  return "Hello {}!".format(name)
 
 
# 不用@的写法
# hello = html_tags('b')(hello)
# html_tags('b') 是一个闭包，它接受一个函数，并返回一个函数
 
print(hello()) # <a>Hello Toby!</a>
print(hello("world")) # <a>Hello world!</a>

def make_printer(msg1, msg2):
  def printer():
    print(msg1, msg2)
  return printer
 
 
printer = make_printer('Foo', 'Bar') # 形成闭包
 
print(printer.__closure__) # 返回cell元组
(<cell at 0x000002721C1D2138: str object at 0x000002721C1F2068>, <cell at 0x000002722B199CD8: str object at 0x000002721C1F20A0>)
print(printer.__closure__[0].cell_contents) # 第一个外部变量'Foo'
print(printer.__closure__[1].cell_contents) # 第二个外部变量'Bar'