Python条件语句与循环

1、判断与循环
python 缩进
main：
print("Hello")
print("Hello world.")

if 判断条件:
    执行语句
elif 判断条件:
    执行语句
else:
    执行语句

while 判断条件:
    执行语句

a = 100
while a>1:
    print(a)
    a-=1
    if a==50:
        break   # 退出循环
    if a==55:
        print("5555555555")
        continue   # 此次循环结束，进入下一个循环

break 跳出循环
continue 进入下一次循环

for item in sequence：
   执行语句

l = ["a","b","c","d","e","f"]
print(l[:])
print(l[0:5])        # 大于等于0     小于5  0 <= a > 5
print(l[0:-1])        # 大于等于0     小于5  0 <= a > 5
for x,y in enumerate(l):    # 打印列表中元素以及下标
    print(x,y)

2、编程思想最重要

编程语言最重要的是思想
ABCD乘以9=DCBA，求A=？，B=？，C=？，D=？

for A in range(1,10):
    for B in range(0,10):
        for C in range(0,10):
            for D in range(1,10):
                start = 1000*A+100*B+10*C+D
                end = 1000*D+100*C+10*B+A
                if start * 9 == end:
                    print("A={}".format(A))
                    print("B={}".format(B))
                    print("C={}".format(C))
                    print("D={}".format(D))
                    print("{0} * 9 = {1}".format(start,end))

返回结果：
A=1
B=0
C=8
D=9
1089 * 9 = 9801

3、求阶乘
求1-n的阶乘的和
1！+ 2！+ 3！+ 4！+5 ！+ ··· + n！
0! = 1
1！= 1
2！= 1 2 = 2
3！= 1 2 * 3 = 6

def one(n):
    total = 1
    if n ==0:
        total = 1
    else:
        for i in range(1,n+1):
            total *= i
    return total
print(one(3))

status=1
while status:
    result = 0
    n= input("Please input a number(n>=0) : ")
    for i in n:
        if not i.isdigit():
            print("The number of you input is error.")
            exit(1)
    if int(n) < 0:
        print("The number of you input is error.")
        break
    for i in range(0,int(n)+1):
        result += one(i)
    print("0! + 1! + 2! + ··· ··· + n! = {}".format(result))