Drop Python 3.6 support

[slel]

This can be a dependency for other tickets.

For instance tickets updating dependencies to
versions that dropped support for Python 3.6.

Related:

• Adopt the “time window-based” policy for support of Python versions from NEP 29 #30384: Adopt "time window-based" Python versions support policy
• Meta-ticket: Review of Python 3 features that sagelib should use systematically #29756: Meta-ticket: Review of Python 3 features that sagelib should use systematically
• Python 3.7+: setlocale: LC_ALL: cannot change locale (C.UTF-8) from build/bin/sage-spkg and in doctests; disable use of system Python 3.6 #30053 - can be dropped if 3.6 is gone

Depends on #30913

CC: @fchapoton @mkoeppe @orlitzky @dimpase @vbraun

Component: python3

Author: Tobias Diez, Matthias Koeppe

Branch/Commit: b06731c

Reviewer: Matthias Koeppe, Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/30551

[mkoeppe]

comment:1

I don't think there is anything that says that we "should" drop Python 3.6 support.

[mkoeppe]

Description changed:

--- 
+++ 
@@ -9,4 +9,4 @@
 Related:
 
 - #30384: Adopt "time window-based" Python versions support policy
-
+- #29756: Meta-ticket: Review of Python 3 features that sagelib should use systematically

[slel]

comment:3

Replying to @mkoeppe:

I don't think there is anything that says
that we "should" drop Python 3.6 support.

Oh good, then let's support it as long as we can.

By the way #15530 and #15980 which started support
for Python 3.6 are almost ready to be closed.

[slel]

Description changed:

--- 
+++ 
@@ -3,9 +3,6 @@
 For instance tickets updating dependencies to
 versions that dropped support for Python 3.6.
 
-And if we adopt the policy in #30384 then
-we should soon drop support for Python 3.6.
-
 Related:
 
 - #30384: Adopt "time window-based" Python versions support policy

[dimpase]

comment:4

#30053 says that we must drop Python 3.6 - unless you want to have a go at it.

it seems that some of our code related to docbuilding is too new for 3.6, and perhaps our Sphinx is too new too.

Besides, the EOL for 3.6 is late 2021, which is soon.

[dimpase]

Description changed:

--- 
+++ 
@@ -7,3 +7,4 @@
 
 - #30384: Adopt "time window-based" Python versions support policy
 - #29756: Meta-ticket: Review of Python 3 features that sagelib should use systematically
+- #30053 - can be dropped if 3.6 is gone

[tobiasdiez]

comment:6

What do you think about adopting the Python version strategy of numpy, according to which "a project with a major or minor version release in November 2020 should support Python 3.7 and newer"?

[mkoeppe]

comment:7

Replying to @tobiasdiez:

What do you think about adopting the Python version strategy of numpy, according to which "a project with a major or minor version release in November 2020 should support Python 3.7 and newer"?

That's #30384

[tobiasdiez]

comment:8

According to NEP 29, "a project with a major or minor version release in November 2020 should support Python 3.7 and newer." and thus this ticket can be closed in my opinion.

(Documentation for following NEP 29 is added in #30384.)

[mkoeppe]

comment:9

??!

This ticket is for dropping support for Python 3.6 -- this involves changing what system python versions we accept (build/pkgs/python3/spkg-configure.m4) and removing python3.6 workarounds from the code.

NEP 29 would already allow us to drop support now -- but I don't think we want to do it now (because of Sage's traditional role of providing a distribution that people can install onto ancient machines) -- hence the milestone is set to "pending".