Python has an extensive standard library ("batteries included!"), but is frequent the necessity of using other modules not included there, mostly from the Python Package Index (PyPI).
The original way of installing those modules is at "system level" (sudo pip install foobar), in the operating system in a general way, making them available to be used by any program that is executed.
Beyond needing root or administrator level to install the dependencies in that way, the first problem we find are conflicts: the typical case of two programs needing two different versions of the same dependency, which can not be achieved when installing the dependencies globally.
This is why is so normal in Python to use "virtual environments" (or "virtualenvs"). A new virtualenv is created for each program, the needed dependencies for each program are installed in the corresponding virtualenv, and as stuff in a virtualenv is only accessible from inside the virtualenv, there are no conflicts anymore.
At this point, however, we hit the problem of the administration of the virtualenvs themselves: create them, install modules in them, activate them to be uses by each program and deactivate them later, remember the names of each environment for each program, etc.
To automatize this, fades was born.
fades allows you to unleash all the power of virtualenvs without needing to worry about them.
Do you want to execute a script that needs the foobar dependency?
fades -d foobar script.py
Do you want an interactive interpreter having foobar installed as
dependency? fades -d foobar
Do you need to execute the script but with several dependencies, one with
a specific version? fades -d foo -d bar -d baz==1.1 script.py
Do you have all the dependencies in a requirements file?
fades -r requirements.txt script.py
These are only simple examples of what you can do with fades. Virtual environments are a very powerful tool, and automate and simplify their use makes fades to have a lot of options, some that you will use everyday, others that will prove useful in some specific situations.
Start to use fades step by step (check the docs) and will find that it will solve the dependencies management in your programs and scripts, using virtualenvs but without the complexity of having to deal with them by hand.