1. 通用装饰器 (同时支持带/不带参数)
通常如果我们想要一个装饰器同时支持带参数和不带参数, 需要编写两个函数来实现. 如下:
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def deco1(func):
def new_func(*args, **kwargs):
# do something
print("No prefix.")
return func(*args, **kwargs)
return new_func
def deco2(prefix=None):
def inner_deco(func):
def new_func(*args, **kwargs):
# do something with `prefix`
print(f"Using prefix: {prefix}")
return func(*args, **kwargs)
return new_func
return inner_deco
@deco1
def foo1():
pass
@deco2(prefix='AAA')
def foo2():
pass
foo1()
foo2()
为了简化代码, 我们可以利用 wrapt.decorator 来简化上面的代码:
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import wrapt
from functools import partial
@wrapt.decorator
def optional_kwargs_decorator(wrapped, instance=None, args=None, kwargs=None):
if args:
return wrapped(*args, **kwargs)
else:
return partial(wrapped, **kwargs)
@optional_kwargs_decorator
def deco(func, prefix=None):
def new_func(*args, **kwargs):
# do something with `prefix`
if prefix is not None:
print(f"Using prefix: {prefix}")
else:
print("No prefix.")
return func(*args, **kwargs)
return new_func
# 不带参数的装饰器, 注意是不加括号的
@deco
def foo1():
pass
# 带参数的装饰器, 以函数的形式调用并传入参数
@deco(prefix='AAA')
def foo2():
pass
foo1()
foo2()
注意上面这段代码中装饰器 optional_kwargs_decorator 如果被 wrapt.decorator 装饰了的话, 其签名是固定的.
虽然上面的代码看起来更复杂了, 但我们额外定义的装饰器 optional_kwargs_decorator 是可以复用的, 它的功能就是令被它装饰的装饰器(这个例子里是 deco)可以同时以带参数和不带参数的形式使用, 而不需要编写两个函数.
2. 常用装饰器
通过在类的方法前面加装装饰器, 可以实现更丰富的类的方法和更简洁的用法.
@property @name.setter
在 python 的类中可以直接把属性暴露在外面, 允许使用者直接查看或者修改, 但是这样就无法对属性设定限制:
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class Student(object):
def __init__(self):
self.score = 0
s = Student()
s.score = 1000
所以为了限制属性不能任意指定, 可以通过接口函数来对属性值进行检查:
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class Student(object):
def __init__(self):
self.score = 0
def get_score(self):
return self.score
def set_score(self, value):
if not isinstance(value, (int, float)):
raise ValueError("Score must be a integer or float.")
if value < 0 or value > 100:
raise ValueError("Score is between 0 and 100")
self.score = value
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>>> s = Student()
>>> s.set_score(60.5)
>>> s.get_score()
60.5
>>> s.set_score(1000)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 10, in set_score
ValueError: Score is between 0 and 100
但是上面要使用两个函数作为接口函数, 调用时十分不方便, 这时就可以使用 property 装饰器, 调用了该装饰器后会自动生成相应的 setter 装饰器:
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class Student(object):
def __init__(self):
self._score = 0
@property
def score(self):
return self._score
@score.setter
def score(self, value):
'setting'
if not isinstance(value, (int, float)):
raise ValueError("Score must be a integer or float.")
if value < 0 or value > 100:
raise ValueError("Score is between 0 and 100")
self._score = value
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>>> s = Student()
>>> s.score
0
>>> s.score = 100
>>> s.score
100
>>> s.score = 1001
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 13, in score
ValueError: Score is between 0 and 100
如果在上面的类中不定义 score.setter 方法, 那么 score 就变成了一个只读属性.