python之控制流

条件判断

简单if语句

>>>name=‘lily‘
>>>if name=‘lily‘:
          print ‘hello,‘, name

hello,lily

if-else

>>>score=90
>>>if score>=80:
          print ‘very good‘
else:
    print ‘keep trying‘

very good

if-elif-else

>>> age=18
>>> if age>=18:
	print ‘adult‘
elif age<18:
	print ‘teenager‘
else:
	print ‘please enter the correct age‘

adult

循环

for

>>> L=[1,2,3,4,5]
>>> for v in L:
	print v

1
2
3
4
5

while

>>> a=0
>>> while a<10:
	a=a+1
	print a

1
2
3
4
5
6
7
8
9
10

退出循环

break与continue区别：

break：退出循环体

利用 while True 无限循环配合 break 语句，计算 1 + 2 + 4 + 8 + 16 + ... 的前20项的和。

>>> s = 0
>>> x = 1
>>> n = 1
>>> while True:
	if n>20:
		break
	s=s+x
	x=x*2
	n=n+1
	print s

1
3
7
15
31
63
127
255
511
1023
2047
4095
8191
16383
32767
65535
131071
262143
524287
1048575

continue：退出本次循环，不执行此次循环的循环体，继续下一个循环

>>> b=[0,1,2,6,3,4,1,5]
>>> for v in b:
	if v<2:
		continue
	print v

2
6
3
4
5