python 条件控制 循环

if

if 语句 if…elif…else…
python 里没有switch…case

if a > 10:
    print('a>10')
elif a < 10:
    print('a<10')
else:
    print('a=10')

while

a = 1
sum = 0

while a <= 100:
    sum += a
    a += 1

print(sum) # 5050

while…else

a = 20

while a<20:
    print('a<20')
else:
    print('a>=20')

# a>=20 

for循环

list1 = [1,2,3,4,5,6,7]

for x in list1:
    print(x) # 1 2 3 4 5 6 7

for…else

list2 = [1,2,3,4,5]

for x in list2:
    print(x)
else:
    print('循环结束')
'''
1
2
3
4
5
循环结束
'''

range()函数
range() 返回一个数列
range(10) : [0,9]
range(5,10) : [5,9]
range(2,10,2) : 2 4 6 8

for x  in range(5):
    print(x) # 0 1 2 3 4

break和continue

break 结束当前循环体,只结束一层
continue 结束当前循环体的本次循环,只结束一层

for a in range(3):
    for b in ['a','b','c','d','e']:
        if b == 'c':
            break
        print( a,'--',b)
'''
0 -- a
0 -- b
1 -- a
1 -- b
2 -- a
2 -- b
'''
for a in range(3):
    for b in ['a','b','c','d','e']:
        if b == 'c':
            continue
        print( a,'--',b)
'''
0 -- a
0 -- b
0 -- d
0 -- e
1 -- a
1 -- b
1 -- d
1 -- e
2 -- a
2 -- b
2 -- d
2 -- e
'''

pass

什么都不执行,python里的占位语句,用来保持代码块的结构完整