python声明函数后边定义的函数_Python--不能不知道的自定义函数

def my_func(message):
    print('Got a message: {}'.format(message))
 
# 调用函数 my_func()
my_func('Hello World')
# 输出
Got a message: Hello World

def name(param1, param2, ..., paramN):
    statements
    return/yield value # optional

def my_sum(a, b):
    return a + b
 
result = my_sum(3, 5)
print(result)
 
# 输出
8

def func(param = 0):
    ...

print(my_sum([1, 2], [3, 4]))
 
# 输出
[1, 2, 3, 4]
 
print(my_sum('hello ', 'world'))
 
# 输出
hello world

def f1():
    print('hello')
    def f2():
        print('world')
    f2()
 
f1()
 
# 输出
hello
world

def connect_DB():
    def get_DB_configuration():
        ...
        return host, username, password
    conn = connector.connect(get_DB_configuration())
    return conn

get_DB_configuration()
 
# 输出
NameError: name 'get_DB_configuration' is not defined

def factorial(input):
    # validation check
    if not isinstance(input, int):
        raise Exception('input must be an integer.')
    if input < 0:
        raise Exception('input must be greater or equal to 0' )
    ...
 
    def inner_factorial(input):
        if input <= 1:
            return 1
        return input * inner_factorial(input-1)
    return inner_factorial(input)
 
 
print(factorial(5))

MIN_VALUE = 1
MAX_VALUE = 10
def validation_check(value):
    if value < MIN_VALUE or value > MAX_VALUE:
        raise Exception('validation check fails')

MIN_VALUE = 1
MAX_VALUE = 10
def validation_check(value):
    ...
    MIN_VALUE += 1
    ...
validation_check(5)
 
##程序报错信息
UnboundLocalError: local variable 'MIN_VALUE' referenced before assignment

MIN_VALUE = 1
MAX_VALUE = 10
def validation_check(value):
    global MIN_VALUE
    ...
    MIN_VALUE += 1
    ...
validation_check(5)

def outer():
    x = "local"
    def inner():
        nonlocal x # nonlocal 关键字表示这里的 x 就是外部函数 outer 定义的变量 x
        x = 'nonlocal'
        print("inner:", x)
    inner()
    print("outer:", x)
outer()
# 输出
inner: nonlocal
outer: nonlocal

def outer():
    x = "local"
    def inner():
        x = 'nonlocal' # 这里的 x 是 inner 这个函数的局部变量
        print("inner:", x)
    inner()
    print("outer:", x)
outer()
# 输出
inner: nonlocal
outer: local

def nth_power(exponent):
    def exponent_of(base):
        return base ** exponent
    return exponent_of # 返回值是 exponent_of 函数
 
square = nth_power(2) # 计算一个数的平方
cube = nth_power(3) # 计算一个数的立方 
square
# 输出
<function __main__.nth_power.<locals>.exponent(base)>
 
cube
# 输出
<function __main__.nth_power.<locals>.exponent(base)>
 
print(square(2))  # 计算 2 的平方
print(cube(2)) # 计算 2 的立方
# 输出
4 # 2^2
8 # 2^3

def nth_power_rewrite(base, exponent):
    return base ** exponent
 

# 不适用闭包
res1 = nth_power_rewrite(base1, 2)
res2 = nth_power_rewrite(base2, 2)
res3 = nth_power_rewrite(base3, 2)
...
 
# 使用闭包
square = nth_power(2)
res1 = square(base1)
res2 = square(base2)
res3 = square(base3)
...