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# Python3.x Python3 Interpreter On Linux/Unix systems, the default Python version is usually 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. This way, 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 systems, you can set the Python environment variable using the following command, assuming your Python is installed in C:Python34: set path=%path%;C:python34 * * * ## 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, then press Enter to see the result: print ("Hello, Python!"); The result of executing 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 condition is True!")... flag condition is True! * * * ## Script-based Programming Copy the following code into a file named **hello.py**: 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 with the following command: $ chmod +x hello.py Execute the following command: ./hello.py The output is: Hello, Python!