Python3 Interpreter

On Linux/Unix systems, the default Python version is generally 2.x. We can install Python3.x in the /usr/local/python3 directory.

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

$ PATH=$PATH:/usr/local/python3/bin/python3    # Set environment variable
$ python3 --version
Python 3.4.0

On Windows, you can set Python’s environment variables using the following command, assuming your Python is installed in C:\Python34:

set path=%path%;C:\python34

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Interactive Programming

We can start the Python interpreter by entering the “Python” command at the command prompt:

$ 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 and press Enter to see the execution result:

print ("Hello, Python!");

The above command produces the following result:

Hello, Python!

When typing a multi-line structure, line continuation is required. Let’s look at the following if statement:

>>> flag = True
>>> if flag :
...     print("flag condition is True!")
... 
flag condition is True!

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Scripted Programming

Copy the following code into a hello.py file:

print ("Hello, Python!");

Execute the script with the following command:

python3 hello.py

The output 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 make it executable:

$ chmod +x hello.py

Execute the following command:

./hello.py

The output is:

Hello, Python!