Python3 Interpreter

On Linux/Unix systems, the default python version is generally 2.x. We can install python3.x in the/usr/local/python3directory.

After installation, we can add the path/usr/local/python3/binto the environment variables of your Linux/Unix operating system, so that you can start Python3 by entering the following command in the shell terminal.

$ PATH=$PATH:/usr/local/python3/bin/python3    # 设置环境变量
$ python3 --version
Python 3.4.0

On Windows systems, you can set Python's environment variables with the following commands, assuming your Python is installed at C:\Python34:

set path=%path%;C:\python34

Interactive Programming

We can enter the "Python" command in the command prompt to start the Python interpreter:

$ python3

After executing the above command, the following window information appears:

$ python3
Python 3.4.0 (default, Apr 11 2014, 13:05:11) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 

Enter the following statement at the python prompt, then press Enter to see the running result:

print ("Hello, Python!");

The execution result of the above command is as follows:

Hello, Python!

When typing a multi-line structure, continuation lines are necessary. Let's look at the following if statement:

>>> flag = True
>>> if flag :
...     print("flag 条件为 True!")
... 
flag 条件为 True!

Script-style Programming

Copy the following code to thehello.pyfile:

print ("Hello, Python!");

Execute the script with the following command:

python3 hello.py

The output result is:

Hello, Python!

On Linux/Unix systems, you can add the following command at the top of the script to make the Python script directly executable like a SHELL script:

#! /usr/bin/env python3

Then modify the script permissions to give it execute permission. The command is as follows:

$ chmod +x hello.py

Execute the following command:

./hello.py

The output result is:

Hello, Python!

Other Extensions