Imports in top-level __init__.py cause eager loading of most enterprise_gateway code

[telamonian]

The top level enterprise_gateway.__init__.py contains a couple of imports that get fired whenever someone imports enterprise_gateway or anything below:

https://github.com/jupyter/enterprise_gateway/blob/443708ffb4cac466fb43e6daccddcdf24aed1945/enterprise_gateway/__init__.py#L4-L5

The from ._version... line is harmless, but the from .enterprisegatewayapp import launch_instance is problematic. Basically, the import from enterprisegatewayapp in turn imports most the rest of the code in the enterprise_gateway pkg, which causes some issues:

• Can help cause large slowdowns when fetching install-wide pkg metadata, eg a particular group of entry points
  • discussed extensively in this ongoing PR about extending entry points to expose jupyter plugins and other resources
• it breaks monkey-patching
  • while not best practice, is currently required for eg overriding builtin TokenAuthorizationMixin

and last (maybe least?)

• it goes against the zen of python

[kevin-bates]

Thanks Max - I was not aware of that side-effect. (The primary maintainers of EG have "cut their teeth" with Python on EG - which may be quite apparent.) That said, EG is derived from Kernel Gateway - which does the same thing. That package is generally lighter in weight, but is this significant enough to warrant a PR there as well?