python学习九--流程控制if for while

亦凉 2022-06-02 01:21 282阅读 0赞

一、条件执行和if语句  
if  条件：  
elif 条件：  
else  
流程控制语句从上到下执行  
=======================  
\[root@node01 python\]\# vi ex04.py       
name =  raw\_input('pls input your name:')  
\#age = int(raw\_input('pls input your age:'))  
\#!/usr/bin/env python  
\#\_\*\_ coding:utf-8 \_\*\_  
name =  raw\_input('pls input your name:')  
\#age = int(raw\_input('pls input your age:'))  
age = input('pls input your age:')  
job = raw\_input('pls input your jor:')  
salary = raw\_input('Salary:')  
print type(age)  
  
if age >30:  
  msg = 'oldold'  
elif age >30:  
  msg = 'old'  
else:  
  msg = 'young'  
  
print  '''  
Personal information of %s:  
  Name: %s  
  Age : %d  
  Job : %s  
  Salay:%s  
\-----------------------  
%s  
''' % (name,name, age,job,salary,msg)  
\[root@node01 python\]\# python ex04.py   
pls input your name:wolf  
pls input your age:40  
pls input your jor:it  
Salary:10  
<type 'int'>  
  
Personal information of wolf:  
  Name: wolf  
  Age : 40  
  Job : it  
  Salay:10  
\-----------------------  
oldold  
================================  
\[root@node01 python\]\# cat ex04.py   
\#!/usr/bin/env python  
\#\_\*\_ coding:utf-8 \_\*\_  
  
name =  raw\_input('pls input your name:')  
\#age = int(raw\_input('pls input your age:'))  
age = input('pls input your age:')  
job = raw\_input('pls input your jor:')  
salary = raw\_input('Salary:')  
print type(age)  
  
if age >30:  
  msg = 'oldold'  
elif age >30:  
  msg = 'old'  
\#else:                         不要这个也不会出错，只是注意下面是否定义变量  
\#  msg = 'young'  
  
print  '''  
Personal information of %s:  
  Name: %s  
  Age : %d  
  Job : %s  
  Salay:%s  
\-----------------------  
%s  
''' % (name,name, age,job,salary,msg)  
\[root@node01 python\]\# python ex04.py     因为上面有变量，所以下面有个错误。  
pls input your name:wolf  
pls input your age:20  
pls input your jor:it  
Salary:10  
<type 'int'>  
Traceback (most recent call last):  
  File "ex04.py", line 27, in <module>  
    ''' % (name,name, age,job,salary,msg)  
NameError: name 'msg' is not defined  
=========================================================  
二、for循环  
for i in rang（1，100）  
\[root@node01 python\]\# vi ex05.py   
\#!/usr/bin/env python  
\#\_\*\_ coding:utf-8 \_\*\_  
name =  raw\_input('pls input your name:')  
\#age = int(raw\_input('pls input your age:'))  
job = raw\_input('pls input your jor:')  
salary = raw\_input('Salary:')  
  
for i in range(3):  
  age = input('pls input your age:')  
  if age >30:  
    print 'think smaller'  
  elif age ==29:  
    print '\\033\[32;1mgood\\033\[0m'  
    break  
  else:  
    print 'think bigger'  
  print 'you still got %s shots!' % (3 - i)  
  
print  '''  
Personal information of %s:  
  Name: %s  
  Age : %d  
  Job : %s  
  Salay:%s  
\-----------------------  
''' % (name,name, age,job,salary)  
\[root@node01 python\]\# python ex05.py   
pls input your name:wolf  
pls input your jor:it  
Salary:25000  
pls input your age:90  
think smaller  
you still got 3 shots!  
pls input your age:20  
think bigger  
you still got 2 shots!  
pls input your age:29  
good  
  
Personal information of wolf:  
  Name: wolf  
  Age : 29  
  Job : it  
  Salay:25000  
\-----------------------  
====================================  
三、while循环  
while True:  
break  
continue  
  
\[root@node01 python\]\# cat while.py   
\#!/usr/bin/env python  
\#\_\*\_ coding:utf-8 \_\*\_  
count = 0  
while True:  
  print 'loop:', count  
  count +=1  
\[root@node01 python\]\# vi while.py       
\#!/usr/bin/env python  
\#\_\*\_ coding:utf-8 \_\*\_  
count = 0  
while count < 100000000:  
  \#print 'loop:', count       这里不打印，很快就显示count值  
  count +=1  
else:  
  print 'loop:', count  
   
\------------------------------------------  
\#!/usr/bin/env python  
\#\_\*\_ coding:utf-8 \_\*\_  
print\_num = input('which loop do you want it to be printed out?')  
count = 0  
while count < 100000000:  
  if count == print\_num:  
    print 'there you got the number:', count  
    choice = raw\_input('do you want to continue the loop?(y/n)')  
    if choice == 'n':  
      break  
    else:  
      while print\_num <= count:  
        if print\_num <= count:  
           print\_num = input('which loop do you want it to be printed out?')  
        else:  
           print u"已经过了，sx!"  
  else:  
    print 'loop:', count    
  count +=1    
      
else:  
  print 'loop:', count    
\[root@node01 python\]\# python while02.py    
which loop do you want it to be printed out?2  
loop: 0  
loop: 1  
there you got the number: 2  
do you want to continue the loop?(y/n)y  
which loop do you want it to be printed out?1  
which loop do you want it to be printed out?2  
which loop do you want it to be printed out?3  
there you got the number: 3  
do you want to continue the loop?(y/n)y  
which loop do you want it to be printed out?4  
there you got the number: 4  
do you want to continue the loop?(y/n)y  
which loop do you want it to be printed out?8  
loop: 5  
loop: 6  
loop: 7  
there you got the number: 8

do you want to continue the loop?(y/n)n

优化上面的代码  
\#!/usr/bin/env python  
\#\_\*\_ coding:utf-8 \_\*\_  
import sys  
  
print\_num = 0  
count = 0  
  
while count < 100000000:  
    if count == print\_num:  
        print 'there you got the number:', count  
        while print\_num <= count:         
            print\_num = input('which loop do you want it to be printed out?')  
            if print\_num == 0:  
                sys.exit('Exit the program!')  
            
            if print\_num <= count:  
                print u"已经过了，sx!"  
               
    else:  
      print 'loop:', count    
    count +=1       
else:  
    print 'loop:', count    
  
============================================  
练习程序  
编写登录接口  
  输入用户名密码  
  认证成功后显示欢迎信息  
  输错三次后锁定  
\[root@node01 python\]\# vi user.py       
\#!/usr/bin/env python  
\#\_\*\_ coding:utf-8 \_\*\_  
import sys  
retry\_limit = 3  
retry\_count = 0  
acccount\_file = 'accounts.txt'  
lock\_file = 'account\_lock.txt'  
while retry\_count < retry\_limit:  
\#只要不超过3次就不断循环  
    username = raw\_input('\\033\[32;1mUsername:\\033\[0m')  
    lock\_check = file(lock\_file)  
    \#当用户输入用户名后，打开lock文件，以检查是否此用户已经lock了  
    for line in lock\_check.readlines():  
    \#循环LOCK文件  
        line = line.split()  
        if username == line\[0\]:  
            sys.exit('\\033\[32;1mUser %s is locked!:\\033\[0m' % usernmae)  
            \#如果LOCK了就直接退出  
    password = raw\_input('\\033\[32;1mPassword:\\033\[0m')  
    f = file(acccount\_file,'rb')  
    \#打开帐号文件  
    match\_flag = False  
    \#默认为False，如果用户match上了，就设置为True  
    for line in f.readlines():  
        user,passwd = line.strip('\\n').split()  
        \#去掉每行多余的\\n并把这一行按空格分成两列，分别赋值为user，passwd两个变量。  
        if username == user and password == passwd:  
        \#判断用户名和密码是否相等  
            print 'Match!', username  
            match\_flag = True  
            \#相等就把循环外的match\_flag变量改为True  
            break  
            \#然后就不用继续循环了，直接跳出，因为已经match上了  
    f.close()  
    if match\_flag == False:  
    \#如果match\_log还为False，代表上面的循环中根本就没有match上用户名和密码，所以需要继续循环。  
        print 'User unmatched!'  
        retry\_count +=1  
    else:  
        print "Welcome login wolf learning system!"  
else:  
    print 'your account is locked!'  
    f = file(lock\_file,'ab')  
    f.write(username)  
    f.close()  
\------------------------------------------------  
import sys  
  
username = 'alex'  
password = 'alex123'  
locked = 1   
retry\_counter = 0  
  
while retry\_counter <3 :  
  user = raw\_input('Username:').strip()  
  if len(user) ==0:  
    print '\\033\[31;1mUsername cannot be empty!\\033\[0m'  
    continue  
  passwd = raw\_input('Password:').strip()  
  if len(passwd) == 0:  
    print '\\033\[31;1mPassword cannot be empty!\\033\[0m'  
    continue  
  \#handle the username and passwd empty issue  
  \#going to the loging verification part  
  if locked == 0:\#means the user is locekd   
    print 'Your username is locked!'  
    sys.exit()  
  else:  
    if user == username  and passwd == password:  
      \#means passed the verfification  
      sys.exit('Welcome %s login to our system!' % user )   
    else:  
      \#retry\_counter = retry\_counter + 1  
      retry\_counter += 1   
      print '\\033\[31;1mWrong username or password, you have %s more chances!\\033\[0m' % (3 - retry\_counter  )  
================================================  
Python文件的readlines()方法使用readline()读取并返回一个包含行的列表直到EOF。  
如果可选的sizehint参数存在，则不读取到EOF，它读取总共大约为sizehint大小的  
字符串(可能在舍入到内部缓冲区大小之后)的整行。  
  
仅在遇到EOF时才返回空字符串。  
  
语法  
以下是readlines()方法的语法 -  
fileObject.readlines( sizehint );  
Python  
参数  
sizehint − 这是要从文件读取的字节数。  
返回值  
  
此方法返回包含行的列表。  
示例  
  
假设’foo.txt‘文件中包含以下行 -  
  
This is 1st line  
This is 2nd line  
This is 3rd line  
This is 4th line  
This is 5th line  
Shell  
以下示例显示了readlines()方法的用法。  
  
\#!/usr/bin/python3  
  
\# Open a file  
fo = open("foo.txt", "r+")  
print ("Name of the file: ", fo.name)  
  
line = fo.readlines()  
print ("Read Line: %s" % (line))  
  
line = fo.readlines(2)  
print ("Read Line: %s" % (line))  
  
\# Close opened file  
fo.close()  
Python  
执行上面代码后，将得到以下结果 -  
  
Name of the file:  foo.txt  
Read Line: \['This is 1st line\\n', 'This is 2nd line\\n',   
   'This is 3rd line\\n', 'This is 4th line\\n', 'This is 5th line\\n'\]  
Read Line: