python--流程控制语句

python流程控制语句

python使用缩进作为其语句分组的方法，建议使用4个空格代替缩进。

(1)if语句：

if expression:

    statement(s)

expression:逻辑值，主要用于判断语句中，用来判断

 -- 一个字符串是否为空

-- 一个运算结果是否为零

-- 一个表达式是否可用

(2)if else语句：

    if expression:

        statement(s)

     else:

        statement(s)

(3)elif语句：

       if expression1:

           statement(s)

       elif expression2:

           statement(s)

       elif expression3:

           statements(s)

       else:

           statement(s)

(4)嵌套的if…elif…else构造

       if expression1:

           statement(s)

           if expression2:

               statement(s)

           else:    

               statements(s)

       else:

           statement(s)

(5)逻辑运算符and or not 结合if else语句进行多条件判断

#!/usr/bin/python

def fun():
return 0

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:
print "B"
elif x>=70:
print "C"
else:
print "bad"
~

(6) for循环

       for iterating_var in sequence:

           statement(s)

       range(i,j,[步进值])

              --如果所创建的对象为整数，可用range

              --i为初始数值

              --j为终止数值，但是不包括在范围内，步进值为可选参数，默认为1

              --i默认为0

#！/usr/bin/python
import time

s="hello"
t=(7,8,9,'x','y')
l=[1,2,3,'a','b']
d={1:111,2:222,5:555,3:333}

for x in range(1,11):
print x
time.sleep(1)
else:
print "ending"

for x in d:
print d[x]
else:
print "ending"

for k,v in d.items():
print k
print v
else:
print "ending"

for x in l:
print x
else:
print "ending"

for x in range(len(s)):
print s[x]
else:
print "ending"

for x in range(1,11):
print x
if x == 3:
pass #代码桩
if x == 2:
print "hello 2"
continue
if x == 5:
exit() #退出程序
if x == 6:
break
print "#"*50 #打印50个#
else:
print "ending" #程序正常结束运行else后的代码

for x in range(1,11):
print "------------>",x

(7)while 循环

       while expression:

           statement(s)

#！/usr/bin/python

x = ""

while x != "q":
print "hello"
x = raw_input("please input something,q for quit:)
if not x：
break
if x == "c":
continue
print "one more time---"
else:
print "ending......"