Drop support for EOL Python 3.4

[hugovk]

Python 3.4 was EOL on 2019-03-16 and deprecated in #6123 and pip 19.0.

The deprecation warning reads:

Python 3.4 support has been deprecated. pip 19.1 will be the last one supporting it. Please upgrade your Python as Python 3.4 won't be maintained after March 2019 (cf PEP 429).

pip 19.2 is coming soon (#6630) so drop support for Python 3.4.

[pradyunsg]

@hugovk Thanks for the PR!

In line with @cjerdonek's suggestion, could you drop all the additional changes (references to 3.4, version based checks etc) and file them as a separate PR?

That way this PR would just be dropping Py3.4 from classifiers, requires error messages etc.

[hugovk]

Thanks for the reviews, updated! Please let me know if I missed something.

[cjerdonek]

Question: if someone happens to be running this pip version using Python 3.4, what should happen? Will it fail? If not, should it log a warning?

[hugovk]

First, python_requires should prevent install on 3.4, for modern pip.

But if someone does end up with this PR's changes on 3.4, it'll still work as no functional changes have been made.

It may fail with the next PR, and will fail at some point in the future as code is modernised and newer features are used.

Would you like an explicit failure message for unsupported versions (<=2.6, 3.0-3.4)? Although care would have to be taken to make sure the file showing the error is still actually compatible with those versions, and it should be tested to be sure it still works in the long term.

What has been the approach for earlier removals?

[pradyunsg]

Would you like an explicit failure message for unsupported versions (<=2.6, 3.0-3.4)?

No point in doing this IMO.

FWIW, modern versions of pip will refuse to install this version on 3.4 anyway. Once you start modifying the distribution, we're not liable for it. 🙃

[chrahunt]

LGTM.

[xavfernandez]

Thanks for doing this.
I'd argue that

pip/tests/conftest.py

Lines 352 to 355 in ca017ca

	@pytest.fixture
	def deprecated_python():
	"""Used to indicate whether pip deprecated this python version"""
	return sys.version_info[:2] in [(3, 4), (2, 7)]

could be included in this PR as it it directly linked to the deprecated call removal but it's ok if it's included in a future PR.

[hugovk]

Is there anything else I can do for this PR?

It'd be nice to get it in this week's pip 19.2, in line with the deprecation message.

Thank you!

[pradyunsg]

Yep yep. This is definitely on my TODO list for the release.

Based on a cursory pass earlier, this seemed good to me. Plus, two folks have already approved it so I'm happy to merge this anyway, based on trust on the contributor + fellow maintainers. 🌈

[pradyunsg]

Thanks for the PR @hugovk!

Thanks for taking the time to look at this @xavfernandez @cjerdonek @chrahunt! :D