In CS41, you'll be writing lots of Python code! Therefore, it's important that you get your development environment ready-to-go as soon as possible.
These instructions are only for Mac OS X and Linux. If you are developing on a Windows computer, see the Installing Python for Windows setup guide.
- Install Python 3.4.3
- Configure
pip - Create a virtual environment
- Install useful packages
Disclaimer: These installation instructions have only been tested on Mac OS X - if you find any errors on Linux, please let us know!
Navigate to the Python 3.4.3 download page, scroll to the bottom (where it says Files) and install the most appropriate distribution of Python.
If you're running OS X 10.6 or higher, you want the Mac OS X 64-bit/32-bit installer. After downloading, double-click the downloaded file, and follow the on-screen instructions.
If you're on Linux, you'll have to build Python from source. Download the source tarball (either gzipped or XZ compressed). Unzip the files and cd into the unzipped directory. To build Python, just execute the usual commands:
$ ./configure
$ make
$ make test
$ sudo make install
More information on the Linux installation process can be found in the README included in the tarball.
Let's check to see if Python is installed correctly!
Run the following from a command prompt:
$ python3
You should see the following:
Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 23 2015, 02:52:03)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
Try writing some Python in the interactive interpreter! When you're done, you can exit the interactive interpreter with CTRL+D or by entering quit() at the Python command prompt.
For CS41, we'll be using a package manager called pip to install and manage Python software packages. By default, Python 3.4.3 ships with a version of pip prebuilt (in our case, pip3 for Python 3). pip interacts very well with PyPI (the Python Package Index), so we'll be using pip extensively this quarter.
First, run the following code at a command prompt. You should see something like the sample output (perhaps different for a different OS)
$ python3 -m pip --version
pip 7.1.2 from /Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages (python 3.4)
If it worked, great! If not, check with a member of the course staff before progressing further.
The following instructions apply to Mac OS X and Linux.
Next, we'll install virtualenvwrapper. This third-party software allows for the creation of isolated Python environments, so there is no conflict in the event that you maintain multiple Python installations on your device. You will need to grant root privileges to the installation script (thus the sudo), so you may need to enter your password.
Note: virtualenvwrapper only works with bash, ksh, and zsh.
$ sudo python3 -m pip install virtualenvwrapper
Collecting virtualenvwrapper
Downloading virtualenvwrapper-4.7.1-py2.py3-none-any.whl
Collecting stevedore (from virtualenvwrapper)
Downloading stevedore-1.12.0-py2.py3-none-any.whl
Collecting virtualenv (from virtualenvwrapper)
Downloading virtualenv-15.0.1-py2.py3-none-any.whl (1.8MB)
100% |████████████████████████████████| 1.8MB 381kB/s
Collecting virtualenv-clone (from virtualenvwrapper)
Downloading virtualenv-clone-0.2.6.tar.gz
Collecting pbr>=1.6 (from stevedore->virtualenvwrapper)
Downloading pbr-1.8.1-py2.py3-none-any.whl (89kB)
100% |████████████████████████████████| 90kB 4.3MB/s
Collecting six>=1.9.0 (from stevedore->virtualenvwrapper)
Downloading six-1.10.0-py2.py3-none-any.whl
Building wheels for collected packages: virtualenv-clone
Running setup.py bdist_wheel for virtualenv-clone
Stored in directory: /Users/<username>/Library/Caches/pip/wheels/<hex_dump>
Successfully built virtualenv-clone
Installing collected packages: pbr, six, stevedore, virtualenv, virtualenv-clone, virtualenvwrapper
Successfully installed pbr-1.8.1 six-1.10.0 stevedore-1.12.0 virtualenv-15.0.1 virtualenv-clone-0.2.6 virtualenvwrapper-4.7.1
Next, we'll need to do some one-time setup to configure the virtual environment for this class.
$ export WORKON_HOME=$HOME/.virtualenvs
$ export VIRTUALENVWRAPPER_PYTHON=`which python3`
This instructs the virtualenvwrapper utility to store all of your virtual environments in the folder .virtualenvs/ in your home directory.
Next, let's see where we installed the virtualenvwrapper.sh script.
On a Mac, the easiest way to do this is with mdfind, which emulates the behavior of Spotlight.
$ mdfind virtualenvwrapper.sh
/Library/Frameworks/Python.framework/Versions/3.4/bin/virtualenvwrapper.sh
/usr/local/bin/virtualenvwrapper.sh
$
Copy the first result to your clipboard. If you see no results, or if you see an error like mdfind: Command not found., try the (slower but also effective) command:
$ find / -name virtualenvwrapper.sh
< ... lots of output ... >
/Library/Frameworks/Python.framework/Versions/3.4/bin/virtualenvwrapper.sh
/usr/local/bin/virtualenvwrapper.sh
$
Copy the first result to your clipboard if you didn't have any luck with mdfind.
If there are no results from the find command, go back and make sure that you have successfully installed virtualenvwrapper. If further problems persist, contact a staff member.
Next, we're going to set up our virtual environment manager:
$ source <path/to/virtualenvwrapper.sh>
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/premkproject
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/postmkproject
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/initialize
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/premkvirtualenv
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/postmkvirtualenv
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/prermvirtualenv
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/postrmvirtualenv
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/predeactivate
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/postdeactivate
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/preactivate
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/postactivate
virtualenvwrapper.user_scripts creating /Users/sredmond/.virtualenvs/get_env_details
where <path/to/virtualenvwrapper.sh> is the path that you found and copied in the previous step.
For example, you might run source /Library/Frameworks/Python.framework/Versions/3.4/bin/virtualenvwrapper.sh or source /usr/local/bin/virtualenvwrapper.sh
In order to make sure everything went smoothly, run workon from the command prompt. This command prints a list of environments, currently empty.
$ workon
$
Now, we'll actually create the virtual environment for CS41. You can name your virtual environment anything you want, but we recommend a short, easy-to-remember name. When you run mkvirtualenv, a new environment is created, and we specify the particular version of Python to use via the --python option.
$ mkvirtualenv --python=`which python3` cs41
Running virtualenv with interpreter /usr/local/bin/python3
Using base prefix '/Library/Frameworks/Python.framework/Versions/3.4'
New python executable in cs41/bin/python3
Also creating executable in cs41/bin/python
Installing setuptools, pip, wheel...done.
virtualenvwrapper.user_scripts creating /Users/<username>/.virtualenvs/cs41/bin/predeactivate
virtualenvwrapper.user_scripts creating /Users/<username>/.virtualenvs/cs41/bin/postdeactivate
virtualenvwrapper.user_scripts creating /Users/<username>/.virtualenvs/cs41/bin/preactivate
virtualenvwrapper.user_scripts creating /Users/<username>/.virtualenvs/cs41/bin/postactivate
virtualenvwrapper.user_scripts creating /Users/<username>/.virtualenvs/cs41/bin/get_env_details
Now, if you run workon, you should see the list of all environments, which now includes cs41.
(cs41)$ workon
cs41
$
You may notice that your command prompt now has the name of the active environment, cs41, printed before it. For example, if your old command prompt was
sredmond:stanfordpython$
your new command prompt would be
sredmond:stanfordpython$ workon cs41
(cs41)sredmond:stanfordpython$
If you see this parenthesized environment name, it means that your environment is active. To deactivate the environment, simply run
(cs41)$ deactivate
$
from a command prompt and you should see the parenthesized environment name disappear.
Let's make sure everything is running smoothly. Run all of the following commands and ensure that the output is appropriate.
# Checking `python`
(cs41)$ which python
/Users/<username>/.virtualenvs/cs41/bin/python
(cs41)$ python --version
Python 3.4.3
(cs41)$ python -c "print('Hello world.')"
Hello world.
# Testing `pip`
(cs41)$ which pip
/Users/<username>/.virtualenvs/cs41/bin/pip
(cs41)$ pip --version
pip 7.1.2 from /Users/<username>/.virtualenvs/cs41/lib/python3.4/site-packages (python 3.4)
Lastly, we'll install some useful packages that will make development a lot easier.
Run the following commands. You should see lots of output, but I've omitted it here.
(cs41)$ pip install --upgrade pip # Make sure `pip` is the newest version
(cs41)$ pip install "ipython[all]" # For ipython interactive interpreter and more
Most relevantly, you should now have access to ipython, an interactive Python interpreter that is vastly superior to the default Python interpreter. You can read an overview here if you'd like. To make sure ipython is configured correctly, run it from a command prompt, and ensure that you get something similar to the below.
(cs41)$ ipython
Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 23 2015, 02:52:03)
Type "copyright", "credits" or "license" for more information.
IPython 4.1.2 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
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Every time you develop code for CS41, you will need to run workon cs41 in order to activate your virtual environment. Again, to deactivate it, you can run deactivate. It might be convenient to add workon cs41 to your shell startup script.
On Mac OS X running bash, you can accomplish this with
$ echo "export WORKON_HOME=$HOME/.virtualenvs" >> ~/.bash_profile
$ echo "export VIRTUALENVWRAPPER_PYTHON=`which python3`" >> ~/.bash_profile
$ echo "source <path/to/virtualenvwrapper.sh>" >> ~/.bash_profile
Additionally, if you want to automatically activate the CS41 virtual environment when you start a new shell session, you can also run:
$ echo "workon cs41" >> ~/.bash_profile
so that workon cs41 is executed at shell startup time.
To see that everything was appended correctly, run
$ tail ~/.bash_profile
< ... possibly some other stuff ... >
export WORKON_HOME=/Users/sredmond/.virtualenvs
export VIRTUALENVWRAPPER_PYTHON=/Library/Frameworks/Python.framework/Versions/3.4/bin/python3
source /Library/Frameworks/Python.framework/Versions/3.4/bin/virtualenvwrapper.sh
workon cs41 # Optional
or something similar.
If you have a different shell startup script (for example, ~/.profile), you will need to append the same line to the end of that startup script.
Try opening a new Terminal / iTerm window, and running workon cs41, python, ipython, and deactivate.
In CS41, we'll be using Sublime Text 3 for development, although Sublime Text 2 will also be fine. You are, of course, free to choose any text editor you please (vim/emacs/nano/xcode/idle/atom/textedit/notepad/etc). On most operating systems, you can provide a default application to open all files of a given type. In our case, you may find it helpful to make every .py file open in Sublime Text.
With <3 by @sredmond