How to use pythonbrew and virtualenv¶

Warning

This is outdated and not longer revelant.

In most of my projects I use virtualenvs and install dependencies by pip, well it’s nothing special, since virtualenvs have become mostly standard in python developement.

But since among my colleagues I’m sort of early-adopter, and I find myself explaining this again and again, I figured that I’ll write this article.

What is a python virtual environment¶

Virtual environment is a way to manage python interpreter and associated installed packages. Generaly you use separate virtualenvs for all your projects, in which case all these projects can depend on different versions of libraries.

Advantages of using virtualenv¶

Projects using different virtualenvs can use different versions of libraries.
To install a library inside virtualenv you don’t need to have root privelages, which is good even if you are root, because packages installed via pip shouldn’t be trusted.

Installing virtualenv¶

Normally you install virtualenv using your system package manager.

Using virtualenv¶

virtualenv foo # create virtualenv in foo subfolder of local folder
New python executable in foo/bin/python
Installing distribute (..) done.
Installing pip...............done.

source foo/bin/activate # Activate the virtualenv

pip install django #install packages
Downloading/unpacking django
  Running setup.py egg_info for package django

    warning: no previously-included files matching '__pycache__' found under directory '*'
    warning: no previously-included files matching '*.py[co]' found under directory '*'
Installing collected packages: django
  Running setup.py install for django
    changing mode of build/scripts-2.7/django-admin.py from 644 to 755

    warning: no previously-included files matching '__pycache__' found under directory '*'
    warning: no previously-included files matching '*.py[co]' found under directory '*'
    changing mode of /tmp/foo/bin/django-admin.py to 755
Successfully installed django
Cleaning up...

python -c 'import django' #Verify django is installed

deactivate # turn off the virtualenv

python -c 'import django' # See that django was installed locally only!
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: No module named django

Used commands

virtualenv path

creates virtualenv in specified path. Interesting options include:

virtualenv –python=python2.5 creates virtualenv using specified interpreter
virtuaelnv –system-site-packages allows virtualenv to use packages installed systemwide (it is nice since some packages can’t be installed easily via pip).

source path/bin/activate

Enables virtualenv in current console

pip install packagename

installs package inside virtualenv (if it was activated)

deactivate

disables virtualenv in current console

Pip cache trick¶

When using virtualenvs you’ll find that installing packages via pip can be painfully slow. You can instruct pip to use cache for downloaded packages by adding following line to your .bashrc file.

export PIP_DOWNLOAD_CACHE=$HOME/.pipcache

Using pythonbrew¶

Virtual enviorment borrows one of your system interpreters, pythonbrew takes it step further: it downloads and compiles your own python interpreter (and has integrated support for virtualenvs.

Installing pythonbrew¶

Dont use instructions from pythonbrew repository, as they basically tell you: ‘download file via http and execute it in bash` (which is very insecure).

Just clone repository stored in github at https://github.com/utahta/pythonbrew and execute install_pythonbrew.py script.

Then as instructed paste following into bashrc file:

[[ -s "$HOME/.pythonbrew/etc/bashrc" ]] && source "$HOME/.pythonbrew/etc/bashrc"

Using pythonbrew¶

pythonbrew install 2.7.1: Installs python 2.7.1 into pythonbrew
pythonbrew use 2.7.1: Use installed python 2.7.1 in current console.
pythonbrew venv create name -p 2.7.1: Create virtualenv named name for python interpreter version 2.7.1
pythonbrew venv use name -p 2.7.1: Activate virtualenv named name for python interpreter version 2.7.1