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04_installation.md

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Installation

Before installing, you must decide which version of Python you want. Both Python 2 and 3 are available from Python.org's official download page.

Installation on Windows

Visit https://www.python.org/downloads/ and download the latest version. The installation is just like any other Windows-based software.

CAUTION: When you are given the option of unchecking any "optional" components, don't uncheck any.

Command Prompt

If you want to be able to use Python from the Windows command prompt (sometimes called the DOS prompt), then you need to set the PATH variable appropriately.

For Windows 2000, XP, 2003 , click on Control Panel -> System -> Advanced -> Environment Variables. Click on the variable named PATH in the System Variables section, then select Edit and add ;C:\Python35 (please verify that this folder exists, it will be different for newer versions of Python) to the end of what is already there. Of course, use the appropriate directory name.

For older versions of Windows, open the file C:\AUTOEXEC.BAT and add the line PATH=%PATH%;C:\Python35 and restart the system. For Windows NT, use the AUTOEXEC.NT file.

For Windows Vista:

  • Click Start and choose Control Panel
  • Click System, on the right you'll see "View basic information about your computer"
  • On the left is a list of tasks, the last of which is Advanced system settings. Click that.
  • The Advanced tab of the System Properties dialog box is shown. Click the Environment Variables button on the bottom right.
  • In the lower box titled System Variables scroll down to Path and click the Edit button.
  • Change your path as need be.
  • Restart your system. Vista didn't pick up the system path environment variable change until I restarted.

For Windows 7 and 8:

  • Right click on Computer from your desktop and select Properties or click Start and choose Control Panel -> System and Security -> System. Click on Advanced system settings on the left and then click on the Advanced tab. At the bottom click on Environment Variables and under System variables, look for the PATH variable, select and then press Edit.
  • Go to the end of the line under Variable value and append ;C:\Python27 (please verify that this folder exists, it will be different for newer versions of Python) to the end of what is already there. Of course, use the appropriate folder name.
  • If the value was %SystemRoot%\system32; It will now become %SystemRoot%\system32;C:\Python35
  • Click OK and you are done. No restart is required, however you may have to close and reopen the command line.

Running the Python prompt on Windows

For Windows users, you can run the interpreter in the command line if you have set the PATH variable appropriately.

To open the terminal in Windows, click the start button and click Run. In the dialog box, type cmd and press [enter] key.

Then, type python (for Python 2) or python3 (for Python 3) and ensure there are no errors.

Installation on Mac OS X

For Mac OS X users, Python 2 is installed by default. You can use Homebrew to get Python 3: brew install python3.

To verify, open the terminal by pressing [Command + Space] keys (to open Spotlight search), type Terminal and press [enter] key. Now, run python (for Python 2) or python3 (for Python 3) and ensure there are no errors.

Installation on GNU/Linux

For GNU/Linux users, Python 2 comes installed by default on most distributions. You can use your distribution's package manager to install Python 3, e.g. on Debian & Ubuntu: sudo apt-get update && sudo apt-get install python3.

To verify, open the terminal by running the "Terminal" or "gnome-terminal" applications (or consult your distro's documentation on starting a terminal). Now, run python (for Python 2) or python3 (for Python 3) and ensure there are no errors.

You can see the version of Python on the screen by running:

$ python -V
Python 2.7.6

$ python3 -V
Python 3.5.1

NOTE: $ is the prompt of the shell. It will be different for you depending on the settings of the operating system on your computer, hence I will indicate the prompt by just the $ symbol.

CAUTION: Output may be different on your computer, depending on the version of Python software installed on your computer.

Summary

From now on, we will assume that you have Python installed on your system.

Next, we will write our first Python program.