Python中的循环退出举例及while

循环退出 

for循环：

for

else

for 循环如果正常结束，都会执行else语句。

脚本1:

    #!/usr/bin/env python

    for i in xrange(10):

        print i

    else:

        print "main end"

结果：

    [root@localhost 20171227]# Python exit.py

    0

    1

    2

    3

    4

    5

    6

    7

    8

    9

    main end

    [root@localhost 20171227]#

脚本2:

    #!/usr/bin/env python

    import time

    for i in xrange(10):

        print i

    time.sleep(1)

    else:

        print "main end"

结果：（中途按ctrl+c中断）

    [root@localhost 20171227]# python exit.py

    0

    1

    2

    3

    4

    ^CTraceback (most recent call last):

    File "exit.py", line 6, in <module>

    time.sleep(1)

    KeyboardInterrupt

    [root@localhost 20171227]#

脚本3:

没正常结束：

    #!/usr/bin/env python

    import time

    for i in xrange(10):

        print i

        if i == 5:

           break

    else:

        print "main end"

结果：

    [root@localhost 20171227]# python exit.py

    0

    1

    2

    3

    4

    5

    [root@localhost 20171227]#

脚本4：（跳过本次循环continue）

    #!/usr/bin/env python

    import time

    for i in xrange(10):

        if i == 3 :

          continue

        if i == 5:

            break

        print i

    else:

        print "main end"

结果：

    [root@localhost 20171227]# python exit.py

    0

    1

    2

    4

    [root@localhost 20171227]#

脚本5:(pass 什么都不作)

    #!/usr/bin/env python

    import time

    for i in xrange(10):

        if i == 3 :

            continue

        elif i == 5:

            break

        elif i ==6:

           pass   #类似shell 中的：

        print i

    else:

        print "main end"

脚本6:

    #!/usr/bin/env python

    import time

    import sys

    for i in xrange(10):

        if i == 3 :

            continue

        elif i == 5:

            continue

        elif i ==6:

            pass

        elif i ==7:

            sys.exit()

        print i

    else:

        print "main end"

    print "hahaha"

结果：

    [root@localhost 20171227]# python exit.py

    0

    1

    2

    4

    6

    [root@localhost 20171227]#

PIP显示第三方包

    [root@localhost 20171227]# pip list

    DEPRECATioN: The default fORMat will switch to columns in the future. You can use --format=(legacy|columns) (or define a format=(legacy|columns) in your pip.conf under the [list] section) to disable this warning.

    backports.ssl-match-hostname (3.4.0.2)

    chardet (2.2.1)

    confiGobj (4.7.2)

    decorator (3.4.0)

    iniparse (0.4)

    IPy (0.75)

    ipython (1.2.1)

    JSONschema (2.5.1)

    kitchen (1.1.1)

    langtable (0.0.31)

    matplotlib (1.2.0)

作业：猜数字游戏

    系统生成一个20以内的随机整数。

    玩家有6次机会进行猜猜看，每次猜测都有反馈（猜大了，猜小了，猜对了-结束）

    6次中，猜对了，玩家赢了。

    否则系统赢了。

    In [1]: import random

    In [2]: random.ran

    random.randint    random.random     random.randrange

    In [2]: random.randint(1,20)

    Out[2]: 14

    In [3]: random.randint(1,20)

    Out[3]: 6

流程控制-while举例

while与for相对比：

    for循环用在有次数的循环上。

    while循环用在有条件的控制上。

while循环：

    while循环，直到表达式变为假，才退出。while循环，表达式是一个逻辑表达式，必须返回一个True或False

语法：

    while expression:

    statement(s)

练习脚本如果下：

脚本1:

    #!/usr/bin/python

    n = 0

    while 1:

        if n == 10:

            break

        print n, 'hellow'

        n +=1

结果：

    [root@localhost 20171227]# python while.py

    0 hellow

    1 hellow

    2 hellow

    3 hellow

    4 hellow

    5 hellow

    6 hellow

    7 hellow

    8 hellow

    9 hellow

    [root@localhost 20171227]# 

脚本2：

    #!/usr/bin/python

    while 1:

        print 'hellow'

        input=raw_input("please input sth,q for exit.")

        if input == "q":

          break

结果：

    [root@localhost 20171227]# python while.py

    hellow

    please input sth,q for exit.s

    hellow

    please input sth,q for exit.3

    hellow

    please input sth,q for exit.q

    [root@localhost 20171227]#

条件 为假时也会退出：

脚本3:

    #!/usr/bin/python

    sth=''

    while sth != 'q':

        print 'hellow'

        sth=raw_input("please input sth,q for exit.")

脚本4:

回车后退出：

    #!/usr/bin/python

    sth=''

    while sth != 'q':

        print 'hellow'

        sth=raw_input("please input sth,q for exit.")

        if not sth:

            break

脚本5:

    #!/usr/bin/python

    sth=''

    while sth != 'q':

        print 'hellow'

        sth=raw_input("please input sth,q for exit.")

        if not sth:

            break

        else:

            print 'world'

结果：

    [root@localhost 20171227]# python while.py

    hellow

    please input sth,q for exit.q

    world

    [root@localhost 20171227]#

脚本6:

#!/usr/bin/python

sth=''

while sth != 'q':

    print 'hellow'

    sth=raw_input("please input sth,q for exit.")

    if not sth:

        break

    if sth == 'quit':

        continue

    print 'continue'

else:

    print 'world'

结果：   

    [root@localhost 20171227]# python while.py    

    hellow

    please input sth,q for exit.ss

    continue

    hellow

    please input sth,q for exit.df

    continue

    hellow

    please input sth,q for exit.quit

    hellow

    please input sth,q for exit.q

    continue

    world