This page explains how to set up Python on a machine so you can run and edit Python programs, and links to the exercise code to download. You can do this before starting the class, or you can leave it until you've gotten far enough in the class that you want to write some code. The Google Python Class uses a simple, standard Python installation, although more complex strategies are possible. Python is free and open source, available for all operating systems from python.org. In particular we want a Python install where you can do two things:
Both of the above are done quite a lot in the lecture videos, and it's definitely something you need to be able to do to solve the exercises.
As a first step, download the google-python-exercises.zip file and unzip it someplace where you can work on it. The resulting google-python-exercises directory contains many different python code exercises you can work on. In particular, google-python-exercises contains a simple hello.py file you can use in the next step to check that Python is working on your machine. Below are Python instructions for Windows and all other operation systems:
Most operating systems other than Windows already have Python installed by default. To check that Python is installed, open a command line (typically by running the "Terminal" program), and cd to the google-python-exercises directory. Try the following to run the hello.py program (what you type is shown in bold):
~/google-python-exercises$ python hello.pyHello World~/google-python-exercises$ python hello.py AliceHello Alice
If python is not installed, see the Python.org download page. To run the Python interpreter interactively, just type python in the terminal:
~/google-python-exercises$ pythonPython 2.5.2 (r252:60911, Feb 22 2008, 07:57:53)[GCC 4.0.1 (Apple Computer, Inc. build 5363)] on darwinType "help", "copyright", "credits" or "license" for more information. >>> 1 + 12>>> you can type expressions here .. use ctrl-d to exit
For Google's Python Class, it's best to use Python 2.7. Although Python 3.x is becoming more popular, this course is designed for Python 2.6 or later.
The commands above are the simplest way to run python programs. If the "execute bit" is set on a .py file, it can be run by name without having to type python first. Set the execute bit with the chmod command like this:
~/google-python-exercises$ chmod +x hello.py~/google-python-exercises$ ./hello.py ## now can run it as ./hello.pyHello World
To install Python on Windows, go to the python.org download page and download Python 2.7.x. Run the Python installer and accept all the defaults. This will install Python in the root directory and set up some file associations.
With Python installed, open a command prompt (Accessories > Command Prompt, or type cmd into the run dialog). Cd to the google-python-exercises directory (from unzipping google-python-exercises.zip). You should be able to run the hello.py python program by typing python hello.py (what you type is shown in bold):
C:\google-python-exercises> python hello.pyHello WorldC:\google-python-exercises> python hello.py AliceHello Alice
If this works, Python is installed. Otherwise, see Python Windows FAQ for help.
To run the Python interpreter interactively, select the Run... command from the Start menu, and type Python -- this will launch Python interactively in its own window. On Windows, use Ctrl-Z to exit (on all other operating systems it's Ctrl-D to exit).
A Python program is just a text file that you edit directly. As above, you should have a command line open, where you can type python hello.py Alice to run whatever exercise you are working on. At the command line prompt, just hit the up-arrow key to recall previously typed commands, so it's easy to run previous commands without retyping them.
You want a text editor with a little understanding of code and indentation. There are many good free ones:
Following are some recommended settings for your text editor:
Here are the preferences to set for common editors to treat tabs and line-endings correctly for Python:
To try out your editor, edit the hello.py program. Change the word "Hello" in the code to the word "Howdy" (you don't need to understand all the other Python code in there - we'll explain it all in class). Save your edits and run the program to see its new output. Try adding a print 'yay!' just below the existing print and with the same indentation. Try running the program, to see that your edits work correctly. For class we want an edit/run workflow that allows you to switch between editing and running easily.
One of the advantages of Python is that it makes it easy to type a little code and quickly see what it does. In class, we want a work setup that matches that: a text editor working on the current file.py, and a separate command line window where you can just press the up-arrow key to run file.py and see what it does.
Teaching philosophy aside: the interpreter is great for little experiments, as shown throughout the lectures. However, the exercises are structured as Python files that students edit. Since being able to write Python programs is the ultimate goal, it's best to be in that mode the whole time and use the interpreter just for little experiments.