color version - PET: Python Entre Todos - Python Argentina

environmentName\Scripts\deactivate.bat
How does virtualenv work
When one creates an environment, inside it three folders are created:
• bin: when one has the environment active, and executes a command like python,
pip or easy_install, one of the binaries in this folder is ran, instead of the system’s.
• include: it’s simply a link to the files installed with Python.
• lib: this is another important folder. Just like include it has a folder named python,
but in contrast to include, this one isn’t a link to the files installed with Python.
Instead, the folder has two important things:
• A link to some Python files. In this case, the .py
• A folder, site-packages, which is where packages are installed when one
uses pip or easy_install
Q & A session (Part 1)
Before I commented that one of the problems we had was that we couldn’t install two
versions of the same library. What I never did is comment how this problem is solved.
The solution is easy. You create a virtual environment to use with django 0.97, and
another for 1.2. You can create as many virtual environments as you wish, and they’re
isolated from each other.
For production servers, there are configurations that can be set up in apache for it to use
some specific virtual environment.
Q & A session (Part 2)
I create a virtualenv, activate it, and do pip freeze, and lots of things that I never
installed appear in the environment.
The default behavior of virtualenv when one creates an environment is to also create it
with the packages one has installed in the system. For it not to do this, when you create
the environment, you can do:
virtualenv --no-site-packages environmentName
This makes it create a completely empty environment. Lastly, another option to note is
—python, which makes the virtual environment use that version of python (it is
necessary to have installed that version for this to work). For instance, in my machine I
have both Python 2.7 and 3.1, being 2.7 the default one.
Thus, when I create an environment, it will be created with Python 2.7. For it to use
Python 3.1, I have to do the following:
virtualenv --python=python3.1 environmentName
Q & A session (Part 3)
There are some packages that have code written in C. What happens with those
Well, in those cases pip or easy_install will try to build the C code when the package is
installed. In distros like Ubuntu, I recommend installing:
• build-essential
• python-dev
Those two packages make it much easier to build.
However, in Windows it is not so easy. Several packages that have C code are distributed
as an .exe too. However, those installers do not allow us to select where to install them.
Here
http://www.developerzen.com/2010/09/23/the-complete-guide-to-setting-up-python-develo
is a very good guide on how to make it build packages as it downloads it.
Q & A session (Part 4)
Do you recommend installing system packages or is it better to use easy_install
There are various distros that come with various python packages that can be installed in
the system. For example:
apt-get python-numpy python-reportlab python-pil
But the versions that can be installed with apt-get are old. Here we’ll see some
comparative examples:
Package name Ubuntu 10.10 version PyPi version
rst2pdf 0.14.2 0.16
reportlab 2.4.3 2.5
django 1.2.3 1.2.3
Thus, it depends on what one wants to do. For instance, if one wants to make a program
work with Ubuntu, then one can create a virtual environment and install the same