Python Learning 1, python Learning

Python Learning 1, python Learning

1. Introduction to python

Introduction to Python on various websites

Python is powerful... and fast;

Plays well with others;

Runs everywhere;

Is friendly & easy to learn;

Is Open.

 

2. python version differences

Short version: Python 2.x is legacy, Python 3.x is the present and future of the language

Python 2.7 is a compatible version, but Python 2.7 wocould be supported until 2020

Print usage is different:

# python 2.xprint "Hello World!"print >>sys.stderr, "fatal error"

# python 3.xprint("Hello World!")print("fatal error", file=sys.stderr)(first,*middle,last) = range(10)

Python 3.x supports Unicode by default, and Python 2.x supports ASCII by default.

When Python 2.x needs to support Chinese characters:

#/Usr/bin/env python #-*-coding: UTF-8-*-print "Hello! "

Python 3.x supports Chinese characters by default:

#/Usr/bin/env pythonprint ("Hello! ")

Python 3.x name changes for some libraries

Old Name	New Name
_ Winreg	Winreg
ConfigParser	Configparser
Copy_reg	Copyreg
Queue	Queue
SocketServer	Socketserver
Markupbase	_ Markupbase
Repr	Reprlib
Test. test_support	Test. support

So. Later, select python 3.x.

 

3. Installation

 

• Install in Windows

• Download the installation package

  https://www.python.org/downloads/

• Install

  Default installation path: C: \ Program Files \ Python35

• Add Environment Variables

  Right-click the computer and choose Properties> advanced system Settings> advanced> environment variables> path> Add path

Example: Add; C: \ Program Files \ Python35; C: \ Program Files \ Python35 \ Scripts

• Linux Installation

• • Download the installation package

Python-3.5.2.tgz

• • Install

Root @ localhost tmp] # tar zxf Python-3.5.2.tgz [root @ localhost tmp] # cd Python-3.5.2 # default installation in the/usr/loca/directory [root @ localhost Python-3.5.2] #. /configure [root @ localhost Python-3.5.2] # make & make install [root @ localhost Python-3.5.2] # python3.5Python 3.5.2 (default, Aug 13 2016, 19:07:36) [GCC 4.8.5 20150623 (Red Hat 4.8.5-4)] on linuxType "help", "copyright", "credits" or "license" for more information. >>>

 

4. the first program

　　Create a hello. py file in the Linux directory and grant permissions to it.

[root@localhost learning]# cat hello.py #!/usr/bin/env pythonprint("Hello World!")[root@localhost learning]# chmod +x hello.py [root@localhost learning]# ./hello.py Hello World!

You can also execute

[root@localhost learning]# pythonPython 3.5.2 (default, Aug 13 2016, 19:07:36) [GCC 4.8.5 20150623 (Red Hat 4.8.5-4)] on linuxType "help", "copyright", "credits" or "license" for more information.>>> print("Hello World!")Hello World!>>>

 

5. Variables

 

VariablesAre used to store information to be referenced and manipulated in a computer program. they also provide a way of labeling data with a descriptive name, so our programs can be understood more clearly by the reader and ourselves. it is helpful to think of variables as containers that hold information. their sole purpose is to label and store data in memory. this data can then be used throughout your program.

• Variable naming rules

• Variable names can only contain uppercase/lowercase letters, numbers, and underscores.

• The variable name cannot start with a number.

• Variable names cannot be the following keywords

  ['And', 'as', 'assert ', 'Break', 'class', 'contine', 'def', 'del ', 'elif ', 'else', 'Got t', 'exec ', 'Finally', 'for ', 'from', 'global', 'if', 'import', 'in ', 'Is ', 'lambda', 'not ',' or ', 'pass', 'print', 'raise ', 'Return', 'try', 'while ', 'with', 'yield ']

 

• Variable declaration and assignment

  Declare a variable named name. The value of the variable name is wenchong.

>>> Name = "wenchong" >>> print (name) wenchong >>># when the variable name1 is assigned a value of name, it is the value of the variable name (that is, the value in memory) assign a value to name1. If the name changes again, the value of name1 will not be affected >>>> name1 = name >>> id (name) 139659587567344 >>> id (name1) 139659587567344 >>>> name = "Jack" >>> id (name) 139659587549592 >>> id (name1) 139659587567344 >>>> print (name, name1) Jack wenchong

 

6. user input

 

1 #!/usr/bin/env python2 # Get User Input String3 name = input("Please Input Name:")4 """5 Python 2.x6 name =  raw_input("Please Input Name:")7 """8 print(name)

Row 1st: Specifies the interpreter.

Row 3: Single Row comment

Row 3-7: multi-line comment

Row 3: Enter the content entered by the user

 

When you enter the password, the password you want to enter is invisible. This module does not take effect in pycharm of windows.

#!/usr/bin/env pythonimport getpasspasswd = getpass.getpass("Please Input Passwd: ")print(passwd)[root@localhost learning]# python hello.py Please Input Passwd: password[root@localhost learning]# 

 

7. Modules

In the python program that captures the input password, one of the actions is import getpass, which is the import module.

• OS Module

OS. mkdir () create a directory

OS. system () is used to execute system commands. The command result cannot be assigned to a variable. Only the return code can be used to assign a value to the variable.

OS. popen () executes the system command. The command result can be assigned to the variable.

# Import module OS >>> import OS >>> OS. mkdir ("testDir") >>> OS. system ("ls-l") total 4-rwxr-xr-x 1 root 238 Aug 13 20:17 hello. pydrwxr-xr-x 2 root 6 Aug 13 20:23 testDir0 >>> command_res = OS. system ("ls-l") total 4-rwxr-xr-x 1 root 238 Aug 13 20:17 hello. pydrwxr-xr-x 2 root 6 Aug 13 20:23 testDir >>> print (command_res) 0 >>> command_res = OS. popen ("ls-l "). read () >>> print (command_res) total 4-rwxr-xr-x 1 root 238 Aug 13 20:17 hello. pydrwxr-xr-x 2 root 6 Aug 13 20:23 testDir

• Sys module

  Sys. path: path list of the python interpreter module

>>> import sys>>> print(sys.path)['', '/usr/local/lib/python35.zip', '/usr/local/lib/python3.5', '/usr/local/lib/python3.5/plat-linux', '/usr/local/lib/python3.5/lib-dynload', '/usr/local/lib/python3.5/site-packages']>>>

• Writing module

  All python files can be used as modules.

[root@localhost learning]# cat mymodel.py #!/usr/bin/env pythonmyname = "Test Model"[root@localhost learning]# pythonPython 3.5.2 (default, Aug 13 2016, 19:07:36) [GCC 4.8.5 20150623 (Red Hat 4.8.5-4)] on linuxType "help", "copyright", "credits" or "license" for more information.>>> import mymodel>>> print(mymodel.myname)Test Model>>>

 

8. Process Control

 

• Scenario 1: user password verification

#! /Usr/bin/env pythonimport getpassusername = "wenchong" passwprd = "pwd123" input_username = input ("Enter the User name:") input_password = getpass. getpass ("Enter password:") if username = input_username and password = input_password: print ("Welcome to heaven... ") else: print (" invalid user name or password ")

• Scenario 2: Guess a number game

#! /Usr/bin/env pythonnumber = 20input_num = int (input ("Please guess a number:") if input_num = number: print ("Congratulations, you guessed it ") elif input_num> number: print ("Please guess a smaller number") else: print ("Please guess a bigger number ")

 

9. Loop

 

• Scenario 1:

  The program will automatically exit after a guess of the number in the previous game, so how can I continue to guess after a guess until the guess is correct?

#! /Usr/bin/env pythonnumber = 20for I in range (10): input_num = int (input ("Please guess a number:") if input_num = number: print ("Congratulations, you guessed it") # If you guessed it, exit the entire loop break elif input_num> number: print ("Please guess a smaller number") else: print ("Please guess a bigger number ")

• Scenario 2:

  After three guesses, the program will prompt whether or not to continue

#! /Usr/bin/env pythonnumber = 20 # define a counter variable count = 0 for I in range (10): # When the counter value is greater than 2, the system prompts whether to continue, if you choose to continue, the counter is reset to 0. Otherwise, the entire loop is exited. if count> 2: user_input = input ("do you want to continue? (Y/n): ") if user_input =" y ": count = 0 continue else: break input_num = int (input (" Please guess a number :")) if input_num = number: print ("Congratulations, you guessed it") break elif input_num> number: print ("guess a smaller number") else: print ("Please guess a bigger number") # execute it once in a loop, that is, to guess a number. Adding 1 # count + = 1 to the counter is equivalent to count = count + 1 count + = 1.