fades 3

What does it do?

fades will automagically create a new virtualenv (or reuse a previous created one), installing the necessary dependencies, and execute your script inside that virtualenv, with the only requirement of executing the script with fades and also marking the required dependencies.

fades can also be executed without passing a child script to execute: in this mode it will open a Python interactive interpreter inside the created/reused virtualenv (taking dependencies from --dependency or --requirement options).

How to execute the script with fades?

You can always call your script directly with fades:

fades myscript.py

However, for you to not forget about fades and to not execute it directly with python, it’s better if you put at the beggining of the script the indication for the operating system that it should be executed with fades…

#!/usr/bin/fades

…and also set the executable bit in the script:

chmod +x yourscript.py

How to mark the dependencies to be installed?

The procedure to mark a module imported by the script as a dependency to be installed by fades is by using a comment.

This comment will normally be in the same line of the import (recommended, less confusing and less error prone in the future), but it also can be in the previous one.

The simplest comment is like:

import somemodule   # fades.pypi
from somepackage import othermodule    # fades.pypi

The fades.pypi is mandatory, it may allow more options in the future.

With that comment, fades will install automatically in the virtualenv the somemodule or somepackage from PyPI.

Also, you can indicate a particular version condition, examples:

import somemodule   # fades.pypi == 3
import somemodule   # fades.pypi >= 2.1
import somemodule   # fades.pypi >=2.1,<2.8,!=2.6.5

Sometimes, the project itself doesn’t match the name of the module; in these cases you can specify the project name (optionally, before the version):

import bs4   # fades.pypi beautifulsoup4
import bs4   # fades.pypi beautifulsoup4 == 4.2

Other ways to specify dependencies

Apart of marking the imports in the source file, there are other ways to tell fades which dependencies to install in the virtualenv.

One way is through command line, passing the --dependency parameter. This option can be specified multiple times (once per dependency), and each time the format is repository::dependency. The dependency may have versions specifications, and the repository is optional (defaults to ‘pypi’).

Other way is to specify the dependencies in a text file, one dependency per line, with each line having the format previously described for the --dependency parameter. This file is then indicated to fades through the --requirement parameter.

In case of multiple definitions of the same dependency, command line overrides everything else, and requirements file overrides what is specified in the source code.

How to control the virtualenv creation and usage?

You can influence several details of all the virtualenv related process.

The most important detail is which version of Python will be used in the virtualenv. Of course, the corresponding version of Python needs to be installed in your system, but you can control exactly which one to use.

No matter which way you’re executing the script (see above), you can pass a -p or --python argument, indicating the Python version to be used just with the number (2.7), the whole name (python2.7) or the whole path (/usr/bin/python2.7).

Other detail is the verbosity of fades when telling what is doing. By default, fades only will use stderr to tell if a virtualenv is being created, and to let the user know that is doing an operation that requires an active network connection (e.g. installing a new dependency).

If you call fades with -v or --verbose, it will send all internal debugging lines to stderr, which may be very useful if any problem arises. On the other hand if you pass the -q or --quiet parameter, fades will not show anything (unless it has a real problem), so the original script stderr is not polluted at all.

Some command line examples

fades foo.py --bar

Executes foo.py under fades, passing the --bar parameter to the child program, in a virtualenv with the dependencies indicated in the source code.

fades -v foo.py

Executes foo.py under fades, showing all the fades messages (verbose mode).

fades -d dependency1 -d dependency2>3.2 foo.py --bar

Executes foo.py under fades (passing the --bar parameter to it), in a virtualenv with the dependencies indicated in the source code and also dependency1 and dependency2 (any version > 3.2).

fades -d dependency1

Executes the Python interactive interpreter in a virtualenv with dependency1 installed.

fades -r requirements.txt

Executes the Python interactive interpreter in a virtualenv after installing there all dependencies taken from the requirements.txt file.

Dependencies

Fades depends on python-xdg package. This package should be installed on any GNU/Linux OS wiht a freedesktop.org GUI. However it is an optional dependency.

You can install it in Ubuntu/Debian with:

apt-get install python-xdg

And on Archlinux with:

pacman -S python-xdg

Fades also needs the virtualenv <https://virtualenv.pypa.io/en/latest/> package to support different Python versions for child execution. (see –python argument.)

It also depends on the pkg_resources package, that comes in with setuptools. Note I didn’t find any system where that is not already included (it’s even there in a clean virtualenv).

For debian/ubuntu

You have a .deb. Download it and install doing:

sudo dpkg -i fades-latest.deb

For Archlinux

We have an AUR package. If you are a yaourt user you can install fades with a simple:

yaourt -S fades

Using pip if you want

pip3 install fades

Multiplatform tarball

Finally you can always get the multiplatform tarball and install it in the old fashion way:

wget http://taniquetil.com.ar/fades/fades-latest.tar.gz
tar -xf fades-latest.tar.gz
cd fades-*
sudo ./setup.py install

Can I try it without installing it?

Yes! Branch the project and use the executable:

git clone https://github.com/PyAr/fades.git
cd fades
bin/fades your_script.py