Laurent Bachelier authored Jul 13, 2018 and hydrargyrum committed Aug 13, 2018

Especially with local_run

Especially for something that trivial

baptiste delpey authored Jun 21, 2017 and Romain Bignon committed Jul 08, 2017

This reverts commit d0a2a6bbe3054a4cb34cf8d5b0bac7e93ac3d509.

raise_from wraps the Python3 syntax "raise exc from cause" which is useful
when an exception is raised to wrap a lower-level exception.

TODO this is less efficient on python2

Some functions changed return type from python2 to python3

TODO: not everything is tested, a full review is needed + run is needed

Using the `nofail` argument and hooking to `login` event, one can make
as much modules unittests as possible run, and skip the unittests which
require authentication or special configuration.

Tests are also run using all available backends now. This is especially
important for modules such as Amazon for which the backend has a large
influence on the website being used and the code being run.

I also changed the default values so that they match the expected type
(rather than being `None`).

This is the same fix than commit "fix parent missing detection and
donwload" (c6cf2b81), but factorized.

It allows a backend to do requests to user by calling a registered
callback function.

In the requests manager, it locks each call to prevent multiple backends
requesting the same think at a time, from an idea of Adrien Clerc.

Closes #945