递归函数

递归

# （非重点）递归：函数return时调用了自己
# n! = [1*2*3...*(n-2)*(n-1)]*n
# = !(n-1)*n
# = !(n-2)*(n-1)*n


# fact 为一个变量
def fact(n):
    if n==1:
        return 1
    return n*fact(n-1)

print(fact(5))      # >>> 120
print(fact(4))      # >>> 24


"""
====> fact(5)
====> 5 * fact(4)
====> 5 * (4 * fact(3))
====> 5 * (4 * (3 * fact(2)))
====> 5 * (4 * (3 * (2 * (fact(1)))))
====> 5 * (4 * (3 * (2 * 1)))
====> 5 * (4 * (3 * 2))
====> 5 * (4 * 6)
====> 5 * 24
====> 120
"""

global

# （了解）global
## (老写法 total是全局变量)从1 加100
# total=0
# for i in range(1,101):
#     total=total+i
# print(total)

## global 显示声明变量为全局变量
total = 0
def add1():
    global total
    total = total + 1

add1()
add1()
add1()
print(total)


# (了解)nonlocal
def outer():
    num = 10
    def inner():
        nonlocal num
        num = 100
        print(num)
    inner()
    print(num)
outer()