装逼利器函数注释

说实话两年来，我从来没有如此的关注过注释，不说话先上代码

def add(a, b) -> 0:
    result = a + b
    add.__annotations__['return'] += result
    return result
print(add.__annotations__['return'])  #0

add(3, 4)
print(add.__annotations__['return'])  #7

add(5, 5)
print(add.__annotations__['return'])  #10

这是python3.3的新的函数注释方式，不支持2，亲试

具体可以有下面三种方式

方式一：  下面的注释参数m:后面是注释，v:后面是注释，->后面是返回值

>>> def kinetic_energy(m:'in KG', v:'in M/S')->'Joules': 
...    return 1/2*m*v**2
... 
>>> kinetic_energy.__annotations__
{'return': 'Joules', 'v': 'in M/S', 'm': 'in KG'}

方式二：注释可以为返回值

>>> rd={'type':float,'units':'Joules','docstring':'Given mass and velocity returns kinetic energy in Joules'}
>>> def f()->rd:
...    pass
>>> f.__annotations__['return']['type']
<class 'float'>
>>> f.__annotations__['return']['units']
'Joules'
>>> f.__annotations__['return']['docstring']
'Given mass and velocity returns kinetic energy in Joules'

　　

方式三： 

def validate(func, locals):
    for var, test in func.__annotations__.items():
        value = locals[var]
        try: 
            pr=test.__name__+': '+test.__docstring__
        except AttributeError:
            pr=test.__name__   
        msg = '{}=={}; Test: {}'.format(var, value, pr)
        assert test(value), msg

def between(lo, hi):
    def _between(x):
            return lo <= x <= hi
    _between.__docstring__='must be between {} and {}'.format(lo,hi)       
    return _between

def f(x: between(3,10), y:lambda _y: isinstance(_y,int)):
    validate(f, locals())
    print(x,y)

　　

>>> f(2,2) 
AssertionError: x==2; Test: _between: must be between 3 and 10
>>> f(3,2.1)
AssertionError: y==2.1; Test: <lambda>

方法总结：

1、在参数后面加注释，可以替代常规默认参数

2、函数名括号后面是返回值对应的value，相当于函数的默认返回值

3、通过__annotations__ 来获取所有的注释信息

通过上面的代码示例，开头代码就总结了几乎所有方法

def add(a:1, b:"aaa") -> 0:
    result = a + b
    add.__annotations__['return'] += result
    return result
print(add.__annotations__['return'])
print(add.__annotations__.items())

add(3, 4)
print(add.__annotations__['return'])

add(5, 5)
print(add.__annotations__['return'])

打印结果：

0
dict_items([('b', 'aaa'), ('return', 0), ('a', 1)])
7
17

为什么这种注释方式我如此的重视？

这种逆天的注释方式，不再是常规的文本方式注释用来解释，而是以一种反射的机制来进行注释，真正做到灵活多变物尽其用

引用官方上面的一句话：

They have the potential to usher in a new era of introspective tools that help developers master more and more complex systems. They also offer the more advanced developer a standard and readable way to associate metadata directly with arguments and return value in order to create custom tools and interact with decorators.