Removing "pkg_resources.get_distribution" usage from pip's codebase

[deveshks]

We have gotten rid of pkg_resources.get_distribution in almost all the places in pip's codebase in #8054 except one.

pip/src/pip/_internal/req/req_install.py

Lines 443 to 468 in 334f06e

	try:
	self.satisfied_by = pkg_resources.get_distribution(str(no_marker))
	except pkg_resources.DistributionNotFound:
	return
	except pkg_resources.VersionConflict:
	existing_dist = get_distribution(
	self.req.name
	)
	if use_user_site:
	if dist_in_usersite(existing_dist):
	self.should_reinstall = True
	elif (running_under_virtualenv() and
	dist_in_site_packages(existing_dist)):
	raise InstallationError(
	"Will not install to the user site because it will "
	"lack sys.path precedence to {} in {}".format(
	existing_dist.project_name, existing_dist.location)
	)
	else:
	self.should_reinstall = True
	else:
	if self.editable and self.satisfied_by:
	self.should_reinstall = True
	# when installing editables, nothing pre-existing should ever
	# satisfy
	self.satisfied_by = None

The idea to get rid of pkg_resources.get_distribution from other places was taken from #8054 (comment) , but this was deferred to a follow-up PR given that the existing PR was already getting big, and it wasn't trivial to update the last function using that construct.

This issue is opened to drive discussion on how to implement the same.

[uranusjr]

I wonder if this is a good time to bring in #8114 as well since they both try to refactor out direct usages of pkg_resources.

[deveshks]

I wonder if this is a good time to bring in #8114 as well since they both try to refactor out direct usages of pkg_resources.

I totally agree. You can now easily replace the custom get_distribution with the implemention in the afore mentioned PR, taking care of the last mention of pkg_resources.get_distribution with that.

[ichard26]

This has been achieved since #8659 (comment).