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

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))

A=1
B=0
C=8
D=9
1089 * 9 = 9801

3、求阶乘

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
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))