color version - PET: Python Entre Todos - Python Argentina

pip freeze > archivoConLibrerias.txt
pip install -r archivoConLibrerias.txt
For example:
• pip install django
• pip install -U rst2pdf
However, there are a few problems:
• You have to have admin/root privileges. It’s easy when you’re developing, but
hardly viable in production.
• You cannot install two versions of the same package.
This is very important when the package isn’t backwards-compatible. Some
examples are:
• SQLAlchemy
• django
For instance, applications that work wit django 0.9.7 won’t work with django 1.2,
and viceversa. Because of the way Python’s package system works, it only allows
one version of any package.
Therefore, one has to choose which version to use.
Using virtualenv
To solve these problems there is virtualenv. It takes care of creating an isolated Python
environment within the system. First, you have to install it:
easy_install virtualenv
This will create a folder environmentName in the directory we’re sitting. If you didn’t
install it into the system, if you downloaded the tarball, then use
python virtualenv.py environmentName
The previous command created a Python environment that is separate from the system’s
global configuration. Therefore, one does not have any permission problems there
because one owns the tree.
To tell the operating system that we want to use the environment we just created, and
not the system’s, it is necessary to activate it.
Linux:
source environmentName/bin/activate
Windows:
environmentName\Scripts\activate.bat
Both in windows and in linux, when you activate an environment, you’ll see the name of
the activated environment between parenthesis:
(environmentName)tzulberti@myhost:~
When you have an active environment, you can see that the python you’re using is not
the global one, but the one inside a folder virtualenv created.
(environmentName)tzulberti@myhost:which python
/home/tzulberti/environmentName/bin/python
This is the only time you’ll need to be root/admin to install a library. All the servers that
allow hosting python projects have it preinstalled.
If you don’t have root/administrator privileges, you can also use it without installing it
into the system. For this, you can download the tarball from:
http://pypi.python.org/pypi/virtualenv
Once installed, the first thing to do is to create a virtual environment:
The same happens with easy_install and pip. Also, any packages installed will be
installed within the virtual environment.
To stop using the environment we have to do the following:
Linux:
deactive
virtualenv environmentName
Windows: