函数

定义：

def add(x, y):
    return x + y

print(add(1, 2))    

空函数

def add():
    pass

参数检查

def add(x, y):
    if not isinstance (x, int):
        raise TypeError('type error with x')
    if not isinstance(y, int):
        raise TypeError('type error with y')
    return x + y

print(add('1', 2))    

返回多个值

def add(x, y):
    # return x, y, 3
    return (x, y, 3)

x, y, z = add(1, 2)
print(x, y, z) # 1, 2, 3

默认参数

def power(x, n = 2):
    s = 1
    while(n > 0):
        s = s * x
        n = n - 1
    return s

print(power(2, 3))    

默认参数必须为不变对象

def add(l = []):
    l.append('end')
    return l

rs = add()
rs = add()
print(rs) # ['end', 'end']

需要改为

def add(l = None):
    if l is None:
        l = []
    l.append('end')
    return l

rs = add()
rs = add()
print(rs)    

可变参数

# 加 *
def calc(*numbers):
    sum = 0
    for n in numbers:
        sum = sum + n
    return sum

print(calc(1, 2, 3))

将 list 转可变参数

def calc(*numbers):
    sum = 0
    for n in numbers:
        sum = sum + n
    return sum

list = [1, 2, 3]    
print(calc(*list)) # 加 *

关键字参数

# kv 前加 **
def person(name, age, **kv):
    return name, age, kv

print(person('fedor', 20, city = 'beijng')) # ('fedor', 20, {'city': 'beijng'})

将 dict 转可关键字参数

def person(name, age, **kv):
    return name, age, kv

map = { 'city': 'beijng', 'tel': '01093897477' }
print(person('fedor', 20, **map)) # map 前加 **

限制关键字参数名字：

def person(name, age, *, city='Beijing', job):
    print(name, age, city, job)

person('Jack', 24, job='Engineer') # Jack 24 Beijing Engineer
person('Jack', 24, job='Engineer', tel = '01000000000') # TypeError: person() got an unexpected keyword argument 'tel'