From https://groups.google.com/forum/#!topic/sage-devel/vYlbnAwKATM "drop python2 compatibility in 9.1" (thread Jan 5-22, 2020).

Removal of Python 2 support in Sage 9.2 has been announced at https://wiki.sagemath.org/Python3-Switch and https://wiki.sagemath.org/ReleaseTours/sage-9.1

Removal tickets:

• For Sage 9.2: Remove python 2 support from sagelib #28000 For Sage 9.2: Remove python 2 support from sagelib
• For Sage 9.2: Remove Python 2 support from the build system and CI scripts #29669 For Sage 9.2: Remove Python 2 support from the build system and CI scripts
• Remove calls to 'long(...)', etc. #27826 - remove long hack for Python 3 in doctest/forker.py, remove all calls to long()
• Remove packages that handle backporting from Python 3 to Python 2 #29754 - remove Python 2 package and packages which backports various parts of Python

Upgrade tickets:

Please check that upgraded packages are compatible with Python >= 3.6 (and note this on the upgrade ticket) because we may wish to support Python 3.6 venv (#29033).

• upgrade to ipython 7 #28197 - upgrade to ipython 7 / prompt-toolkit 2. See also Sort dictionaries for doctests independent of ipythons pretty print #29042
• Upgrade: Python 3.8.5 #27754 - Upgrade: Python 3.8.x (see #27754 comment:55 in particular)
• numpy >= 1.17 - Upgrade NumPy to 1.18.5, scipy to 1.4.1, add pybind11 package #29425 Upgrade Cython to 0.29.16, NumPy to 1.18.2 to fix numpy build error on local-conda-forge-macos-standard
• Update sympy to 1.6 #29730 Update sympy to 1.6
• matplotlib-3: Update to matplotlib 3 #29547. Related: Messed up labels in crystal plot #28449 and #27866 comment:25
• sphinx-2: Update to sphinx 3 #28856, Fix sphinxify deprecation warnings with sphinx 2.2 #29095
• scipy-1.3+: Fix deprecation warnings with scipy 1.4 #29115
• rpy2 3.x: Support rpy 3.x #28988, upgrade rpy2 package 2.8.2 -> 3.3.5, upgrade R to 3.6.3, add new dependencies #29441
• networkx 2.4: networkx 2.3 compatibility #28450
• Upgrade setuptools, setuptools_scm, pip (2020-06), add package wheel; remove zope_interface #29803 - Upgrade setuptools, setuptools_scm, pip

Other:

• compatibility with python 3.8... needs details
  • "at this point the major issues are python 3.8 and ipython 7, and I don't see how one could support several versions of them without forking hundreds of doctests. Both updates require multi-thousand-lines patches, due to changes in dict sorting and hashes."
• remove src/sage/cpython/_py2_random.py
  • This was added in py3: problems with tests that use random_element #24508 and is only used during doctesting in order to ensure consistent random results between Python 2 and 3.

Reference: Tickets that kept Python 2 compatibility but introduced a performance penalty for Python 2:

• get rid of part of itervalues #29103 (get rid of part of itervalues)

See also:

• 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

CC: @fchapoton @embray @jdemeyer @slel @antonio-rojas @kiwifb @timokau @jhpalmieri @tscrim @isuruf @nbruin @orlitzky @vbraun @dimpase @videlec @kliem

Component: python3

Keywords: sd109

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/29141