Starting a new python project

When I start a new python project (no matter how small) I use virtualenv (actually virtualenvwrapper) to ensure a clean enviroment, git for version control and generally Sublime Editor 2.

1. Install virtualenv and virtualenvwrapper.

$ sudo apt-get install python-pip
$ sudo pip install virtualenvwrapper

virtualenvwrapper adds a bunch of functionality to virtualenv, the following two commands are the most useful, and are covered in this guide.:

$ mkproject
$ workon

1a. Setting up virtualenvwrapper.

virtualenvwrapper requires two enviroment variables to be setup.:

$ export WORKON_HOME="/home/pfarmer/py"
$ export PROJECT_HOME="/home/pfarmer/projects"

WORKON_HOME is the directory in which the virtual enviroments will be created, PROJECT_HOME is the directory in which your project folders will be created. It is advisable to put these variables in your profile.

2. mkproject.

mkproject creates a virtual enviroment and a project folder, it then moves into the project and activates the virtual enviroment.:

$ mkproject testproject1
New python executable in testproject1/bin/python
Installing setuptools............done.
Installing pip...............done.
virtualenvwrapper.user_scripts creating /home/pfarmer/py/testproject1/bin/predeactivate
virtualenvwrapper.user_scripts creating /home/pfarmer/py/testproject1/bin/postdeactivate
virtualenvwrapper.user_scripts creating /home/pfarmer/py/testproject1/bin/preactivate
virtualenvwrapper.user_scripts creating /home/pfarmer/py/testproject1/bin/postactivate
virtualenvwrapper.user_scripts creating /home/pfarmer/py/testproject1/bin/get_env_details
Creating /home/pfarmer/projects/testproject1
Setting project for testproject1 to /home/pfarmer/projects/testproject1

Notice that pip and setuptools are installed by default and your command prompt is modified to indicate the project you are currently working on.

3. workon.

workon activates an already created project and moves to the project folder.:

$ workon testproject1

3a. deactivate.

When you have finished working on a project, you can use the “deactivate” command to turn off the virtual enviroment.:

(testproject1)$ deactivate

4. Installing packages into the virtual enviroment with pip.

So, we now have a project called testproject1, lets install some python packages into it. In this case we’re going to install the web micro framework flask.:

(testproject1)$ pip install flask
Downloading/unpacking flask
  Downloading Flask-0.8.tar.gz (494Kb): 494Kb downloaded
  Running egg_info for package flask


Successfully installed flask Werkzeug Jinja2
Cleaning up...

Notice how pip actually installed three packages, flask + Werkzeug and Jinja2, Werkzeug and Jinja2 are dependancies for flask. Alternately you can add packages to a “requirements” file.:

(testproject1)$ echo flask >> requirements.txt
(testproject1)$ pip install -r requirements.txt
Downloading/unpacking flask
  Downloading Flask-0.8.tar.gz (494Kb): 494Kb downloaded
  Running egg_info for package flask


Successfully installed flask Werkzeug Jinja2
Cleaning up...

Using a requirements file makes you project much more portable, you can just zip up your project folder, take it anywhere, once unzipped in the new location you can run pip install -r requirements and you have every package you need.

5. Create a small application.

#!/usr/bin/env python
from flask import Flask
app = Flask(__name__)

def hello():
    return "Hello World!"

if __name__ == "__main__":

Save this file as “”, now run ”./” and browse to http://localhost:5000/ to see your app in action.

6. Using git.

I can’t extol the importance of source control enough, even for small projects, the ability to roll back a change you have made to source code is invaluable! At the very least you should zip up your project before any change, so you can revert, but I think you’ll find that using git to manage your source code is much better.

7. Create the git repository.

(testproject1)$ cdproject
(testproject1)$ git init .
(testproject1)$ git add -A
(testproject1)$ git commit -m "initial commit"

I keep my projects folder inside a Dropbox folder, this has several benefits for me:

  • All my repositories are automatically backed up.
  • My code stays in the sync between several computers.

But you might find that a public repository on github is what you need, is which case do the following::

(testproject1)$ git remote add origin
(testproject1)$ git push -u origin master

8. My git workflow.

As most of my projects have just me working on them, I use a fairly simple workflow. Generally my repositories consist of two branches:

$ git branch
* dev

master is the standard branch, and this is where my “stable” code lives. dev is where I generally work, once I’m happy with my code in dev I merge into master, which is generally a fast-forward merge.

If I’m making major changes, then I will use a feature branch which is branched off dev. My commits might typically look like this::

master     a -------- d ------------------- h -------------- m
            \        /                     /                /
dev          b ---- c ---- e ---- f ---- g ---- i -------- l
                                                 \        /
feature x                                         j ---- k

In this example a is the initial commit, b and c are commits into the dev branch, d is the point at merge b and c merge back into master, e, f and g are commits in dev, h is the merge into master, i is a commit in dev, j and k are commits in branch feature x based off i, l is the merge of feature x into dev and m is the merge of l into master.

But my commit history could look like this::

master     a --------------------------- g ------------ l
            \           \               /             /
dev          b ---- cx   d ---- e ---- f ---- j ---- k
feature x                                h ---- ix

In this example, b and cx are commits made to dev, but at commit cx I abandoned the changes, commit d is a fresh dev branch from commit a, h and ix are commits to the “feature x” branched from commit f on dev being abandoned at commit ix.

As you can see, using git like this gives me huge amounts of flexibility to write experimental code without worrying about being able to get back to a known good point in my code.

9. Commit early, commit often.

Using this workflow you can commit often, making small incremental changes to you code, at the point at which you want to merge code back into your dev or master branches you can squash any number of commits, combining the changes and log messages, typically grouping squashed commits together based on the change they represent.