python高阶函数functools模块的具体使用

# 累加
reduce(lambda x,y:x+y, [1,2,3,4]) # 10

# 逆序字符串
reduce(lambda x,y:y+x, 'abcdefg') # 'gfedcba'

def add(a, b, note="add"):
    result = a + b
    print(f"{note} result: {result}")
    return result

add3 = functools.partial(add, 3)
add5 = functools.partial(add, 5, note="partialed")

print(add3(1)) # add result: 4
print(add3(2, note="partial3")) # partial3 result: 5
print(add5(3)) # partialed result: 8

class Cell(object):
    def __init__(self):
        self._alive = False

    @property
    def alive(self):
        return self._alive

    def set_state(self, state):
        self._alive = bool(state)

    set_alive = functools.partialmethod(set_state, True)
    set_dead = functools.partialmethod(set_state, False)

c = Cell()
print(c.alive)  # False

c.set_alive()
print(c.alive)  # True

def wrapper_decorator(func):
    @functools.wraps(func) # 若是去掉此wraps，则被装饰的函数名称与说明都变为此函数的
    def wrapper(*args, **kwargs):
        """doc of decorator"""
        print('in wrapper_decorator...')
        return func(*args, **kwargs)

    return wrapper

@wrapper_decorator
def example():
    """doc of example"""
    print('in example function')

example()
# in wrapper_decorator...
# in example function
print(example.__name__, "; ", example.__doc__) # example ;  doc of example

# 缺省匹配类型，注册object类型（与后续注册类型都不匹配时使用）
@functools.singledispatch
def show_dispatch(obj):
    print(obj, type(obj), "dispatcher")

# 匹配str字符串
@show_dispatch.register(str)
def _(text):
    print(text, type(text), "str")

# 匹配int
@show_dispatch.register(int)
def _(n):
    print(n, type(n), "int")

# 匹配元祖或者字典
@show_dispatch.register(tuple)
@show_dispatch.register(dict)
def _(tup_dic):
    print(tup_dic, type(tup_dic), "tuple/dict")

### 打印注册的类型：
# dict_keys([<class 'object'>, <class 'str'>, <class 'int'>, <class 'dict'>, <class 'tuple'>])
print(show_dispatch.registry.keys())

show_dispatch(1)
show_dispatch("xx")
show_dispatch([1])
show_dispatch((1, 2, 3))
show_dispatch({"a": "b"})
# 1 <class 'int'> int
# xx <class 'str'> str
# [1] <class 'list'> dispatcher
# (1, 2, 3) <class 'tuple'> tuple/dict
# {'a': 'b'} <class 'dict'> tuple/dict

test = [1, 3, 5, 2, 4]
test.sort(key=functools.cmp_to_key(lambda x, y: 1 if x < y else -1))
print(test) # [5, 4, 3, 2, 1]

@functools.total_ordering
class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __lt__(self, other):
        if isinstance(other, Person):
            return self.age < other.age
        else:
            raise AttributeError("Incorrect attribute!")

    def __eq__(self, other):
        if isinstance(other, Person):
            return self.age == other.age
        else:
            raise AttributeError("Incorrect attribute!")

mike = Person("mike", 20)
tom = Person("tom", 10)

print(mike < tom)
print(mike <= tom)
print(mike > tom)
print(mike >= tom)
print(mike == tom)