Use a callable to define fixture scoped dynamically #1682
Description
Allow scope parameter of fixtures to receive a callable instead of a string. When a callable, it will be called with the config object (passed as keyword argument) and should return a string, which will determine the scope of the fixture. This function will evaluate only once.
The idea is that developers might be interested to have different scopes for a fixture depending on a command line option, so that one might choose to change a fixture scope to session to avoid costly initialization during development, but opt to change it to function in a C.I. server.
Suggested by @hpk42