python学习笔记二：流程控制

一、if else：

#!/usr/bin/python
x = int(raw_input('please input:'))

if x >= 90:
    if x >= 95:
        print 'a+'
    else:
        print 'a'
elif x >= 80:
    if x >= 85:
        print 'b+'
    else:
        print 'b'
elif x >= 70:
    if x >= 75:
        print 'c+'
    else:
        print 'c'
else:
    if x >= 60:
        print 'd+'
    else:
        print 'bad'

二、逻辑运算符 and or not

#!/usr/bin/python
x = int(raw_input('please input x:'))
y = int(raw_input('please input y:'))

if x >= 90 and y >= 90:
    print 'a'
elif x >= 80 or y >= 80:
    print 'b'
elif not x < 60 and (not y < 60):
    print 'c'
else:
    print 'bad'

三、for

序列：

#!/usr/bin/python

s = "hello python"

for x in s:
    print x

for index in range(len(s)):
    print s[index]

字典：

#!/usr/bin/python

dic = {'a':1,'b':2,'c':3}

for x in dic:
    print x,dic[x]

for k,v in dic.items():
    print k,v

控制

else：for正常执行完会执行else中的内容，否则不会（如下面的代码执行过程按Ctrl+c）

#!/usr/bin/python
import time

for x in range(10):
    print x
    time.sleep(1)
else:
    print 'end'

break：跳出当前这层循环

#!/usr/bin/python
for x in range(10):
    print x
    if x == 6:
        break
else:
    print 'end'

这里不会执行else中的内容

pass：占位

exit：退出

#!/usr/bin/python
for x in range(10):
    print x
    if x == 2:
        print 'hello',x
        continue
    if x == 4:
        pass
    if x == 5:
        exit()
    if x == 6:
        break
    print '*'*10
else:
    print 'end'

四、while

当条件失败，正常结束会执行，执行break后else中不执行

#!/usr/bin/python

x = 'hello'

while x != "q":
    print x
    x = raw_input('please input something,q for quit:')
    if not x:
        break
else:
    print 'ending'