流程控制--while

Posted 2020-08-06 Frankiee

/* while 是在有条件控制的情况下 进行的循环 */
[[email protected] test1]# vim 13.py
//ADD
#!/usr/bin/python

n = 0
while True:
    if n == 10:
        break
    print n, ‘hello‘
    n += 1

[[email protected] test1]# python 13.py
0 hello
1 hello
2 hello
3 hello
4 hello
5 hello
6 hello
7 hello
8 hello
9 hello

 

[[email protected] test1]# vim 14.py
//ADD
#!/usr/bin/python

while True:
    print ‘hello‘
    input = raw_input("Please input something.q for quit: ")
    if input == "q":
        break

[[email protected] test1]# python 14.py
hello
Please input something.q for quit: e
hello
Please input something.q for quit: r
hello
Please input something.q for quit: t
hello
Please input something.q for quit: f
hello
Please input something.q for quit: q

 

[[email protected] test1]# vim 15.py
//add
#!/usr/bin/python

x = ‘‘
while x != ‘q‘:
    print ‘hello‘
    x = raw_input("Please input something, q for quit: ")

/* 首先，要给x定义一个初始值，

    然后再继续执行。 这里没有定义输入q后会有什么结果，

    但是执行后，输入q则自动退出
*/

[[email protected] test1]# python 15.py
hello
Please input something, q for quit: s
hello
Please input something, q for quit: s
hello
Please input something, q for quit: d
hello
Please input something, q for quit: f
hello
Please input something, q for quit: g
hello
Please input something, q for quit: q

 

/* 先创建一个文件 */
[[email protected] tmp]# cat 1.txt
1111

//先用一个变量定义，这个变量对应什么文件
In [1]: ll = open(‘/tmp/1.txt‘)

In [2]: ll
Out[2]: <open file ‘/tmp/1.txt‘, mode ‘r‘ at 0x99d81d8>

//将这个文件或变量打开，并赋予w权限
In [4]: ll = open(‘/tmp/1.txt‘, ‘w‘)

//写变量。括号里为写的内容，此处写的内容会覆盖原来的内容
In [5]: ll.write("aa")

[[email protected] tmp]# cat 1.txt
aa[[email protected] tmp]#

/* 有时，需要需要将变量关掉才可以执行看到改变 */

/* 再一次打开python的界面需要重新定义变量。*/
In [2]: ll = open(‘/tmp/1.txt‘)

In [3]: ll.read()　　　　//从最开始读
Out[3]: ‘aa‘

In [4]: ll.read()　　　　//当第二次读取时，指针已经读完了前面的内容，就只剩空了
Out[4]: ‘‘

 

/* 读取的具体内容 */

//1. 输入需要读取的 前几个字符
[[email protected] tmp]# cat 1.txt
abc
sjdh[[email protected] tmp]#

In [1]: ll = open(‘/tmp/1.txt‘ , ‘r‘)

In [2]: ll
Out[2]: <open file ‘/tmp/1.txt‘, mode ‘r‘ at 0x9392180>

In [3]: ll.read(2)
Out[3]: ‘ab‘

// 2.读取一行
In [1]: ll = open(‘/tmp/1.txt‘)

In [2]: ll.readline()
Out[2]: ‘abc\n‘

// 3.读取多行（有多少行读多少行），并且返回一个list


// 4. next() 可对一个文件一行一行的读取
In [5]: ll = open(‘/tmp/1.txt‘)

In [6]: ll.readlines()
Out[6]: [‘abc\n‘, ‘sjdh‘]

In [1]: ll = open(‘/tmp/1.txt‘)

In [2]: ll.next()
Out[2]: ‘abc\n‘

In [3]: ll.next()
Out[3]: ‘sjdh‘

In [4]: ll.next()
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
<ipython-input-4-e9a4e3e4293f> in <module>()
----> 1 ll.next()

StopIteration:

 

 

/* python脚本，对文件进行遍历 */

[[email protected] test1]# vim 16.py
//ADD
#!/usr/bin/python

ll = open(‘/tmp/1.txt‘)
for line in ll.readlines():
    print line,

[[email protected] test1]# python 16.py
abc
sjdh