Importing pkg_resources is slow. Work is done at import time. #926
Description
Any "import pkg_resources" by a module is slow, in the 100-150ms range, depending on the system.
This is due to the number of modules imported by pkg_resources itself (email.parser is also slow), and side-effect work done at import time, notably the _initialize and _initialize_master_working_set functions at the bottom of pkg_resources/__init__.py.
As wall clock time matters to humans running CLIs, every millisecond counts.
The work done at import time should be deferred until needed, and the imports themselves also deferred if possible.