我如何在Python中制作两个装饰器来完成以下操作?

@make_bold
@make_italic
def say():
   return "Hello"

调用say()应返回:

"<b><i>Hello</i></b>"

当前回答

下面有make_bold()和make_italic():

def make_bold(func):
    def core(*args, **kwargs):
        result = func(*args, **kwargs)
        return "<b>" + result + "</b>"
    return core

def make_italic(func):
    def core(*args, **kwargs):
        result = func(*args, **kwargs)
        return "<i>" + result + "</i>"
    return core

您可以使用say()将它们用作装饰器,如下所示:

@make_bold
@make_italic
def say():
   return "Hello"

print(say())

输出:

<b><i>Hello</i></b>

当然,您可以直接使用make_bold()和make_italic()而不使用修饰符,如下所示:

def say():
    return "Hello"
    
f1 = make_italic(say)
f2 = make_bold(f1)
result = f2()
print(result)

简而言之:

def say():
    return "Hello"
    
result = make_bold(make_italic(say))()
print(result)

输出:

<b><i>Hello</i></b>

其他回答

或者,您可以编写一个工厂函数,该函数返回一个装饰器,该装饰器将装饰函数的返回值包装在传递给工厂函数的标记中。例如:

from functools import wraps

def wrap_in_tag(tag):
    def factory(func):
        @wraps(func)
        def decorator():
            return '<%(tag)s>%(rv)s</%(tag)s>' % (
                {'tag': tag, 'rv': func()})
        return decorator
    return factory

这使您能够编写:

@wrap_in_tag('b')
@wrap_in_tag('i')
def say():
    return 'hello'

or

makebold = wrap_in_tag('b')
makeitalic = wrap_in_tag('i')

@makebold
@makeitalic
def say():
    return 'hello'

就我个人而言,我会用不同的方式来编写装饰器:

from functools import wraps

def wrap_in_tag(tag):
    def factory(func):
        @wraps(func)
        def decorator(val):
            return func('<%(tag)s>%(val)s</%(tag)s>' %
                        {'tag': tag, 'val': val})
        return decorator
    return factory

这将产生:

@wrap_in_tag('b')
@wrap_in_tag('i')
def say(val):
    return val
say('hello')

不要忘了decorator语法是一种简写的构造:

say = wrap_in_tag('b')(wrap_in_tag('i')(say)))

考虑下面的修饰符,注意我们将wrapper()函数作为对象返回

def make_bold(func):
    def wrapper():
        return '<b>'+func()+'</b>'
    return wrapper

所以这个

@make_bold
def say():
    return "Hello"

计算结果为

x = make_bold(say)

注意,x不是say(),而是在内部调用say(()的包装器对象。这就是装饰师的工作原理。它总是返回调用实际函数的包装器对象。如果链接此

@make_italic
@make_bold
def say():
    return "Hello"

转换为此

x = make_bold(say)
y = make_italic(x)

以下是完整的代码

def make_italic(func):
    def wrapper():
        return '<i>'+func()+'</i>'
    return wrapper


def make_bold(func):
    def wrapper():
        return '<b>'+func()+'</b>'
    return wrapper


@make_italic
@make_bold
def say():
    return "Hello"


if __name__ == '__main__':
    # x = make_bold(say) When you wrap say with make_bold decorator
    # y = make_italic(x) When you also add make_italic as part of chaining
    # print(y())
    print(say())


上述代码将返回

<i><b>Hello</b></i>

希望这有帮助

做同样事情的另一种方式:

class bol(object):
  def __init__(self, f):
    self.f = f
  def __call__(self):
    return "<b>{}</b>".format(self.f())

class ita(object):
  def __init__(self, f):
    self.f = f
  def __call__(self):
    return "<i>{}</i>".format(self.f())

@bol
@ita
def sayhi():
  return 'hi'

或者,更灵活地说:

class sty(object):
  def __init__(self, tag):
    self.tag = tag
  def __call__(self, f):
    def newf():
      return "<{tag}>{res}</{tag}>".format(res=f(), tag=self.tag)
    return newf

@sty('b')
@sty('i')
def sayhi():
  return 'hi'
#decorator.py
def makeHtmlTag(tag, *args, **kwds):
    def real_decorator(fn):
        css_class = " class='{0}'".format(kwds["css_class"]) \
                                 if "css_class" in kwds else ""
        def wrapped(*args, **kwds):
            return "<"+tag+css_class+">" + fn(*args, **kwds) + "</"+tag+">"
        return wrapped
    # return decorator dont call it
    return real_decorator

@makeHtmlTag(tag="b", css_class="bold_css")
@makeHtmlTag(tag="i", css_class="italic_css")
def hello():
    return "hello world"

print hello()

也可以在类中编写decorator

#class.py
class makeHtmlTagClass(object):
    def __init__(self, tag, css_class=""):
        self._tag = tag
        self._css_class = " class='{0}'".format(css_class) \
                                       if css_class != "" else ""

    def __call__(self, fn):
        def wrapped(*args, **kwargs):
            return "<" + self._tag + self._css_class+">"  \
                       + fn(*args, **kwargs) + "</" + self._tag + ">"
        return wrapped

@makeHtmlTagClass(tag="b", css_class="bold_css")
@makeHtmlTagClass(tag="i", css_class="italic_css")
def hello(name):
    return "Hello, {}".format(name)

print hello("Your name")

装饰只是语法上的糖。

This

@decorator
def func():
    ...

扩展到

def func():
    ...
func = decorator(func)