Trac #30551: Drop Python 3.6 support

This can be a dependency for other tickets.

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

Related:

- #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

URL: https://trac.sagemath.org/30551
Reported by: slelievre
Ticket author(s): Tobias Diez, Matthias Koeppe
Reviewer(s): Matthias Koeppe, Dima Pasechnik

build/bin/sage-bootstrap-python

@@ -30,15 +30,6 @@ fi
 # is accessible by this python; this is to guard on Cygwin against Pythons
 # installed somewhere else in Windows.
 
-# Trac #30008: Make it work even if the environment tries to sabotage UTF-8
-# operation in Python 3.0.x-3.6.x by setting LC_ALL=C or similar.
-
-if [ "$LC_ALL" = "C" -o "$LANG" = "C" -o "$LC_CTYPE" = "C" ]; then
-    LC_ALL=$(locale -a | grep -E -i '^(c|en_us)[-.]utf-?8$' | head -n 1)
-    LANG=$LC_ALL
-    export LC_ALL
-    export LANG
-fi
 
 PYTHONS="python python3 python3.8 python3.7 python2.7 python3.6 python2"
 for PY in $PYTHONS; do

build/bin/sage-site

@@ -149,12 +149,7 @@ if [ "$1" = "-docbuild" -o "$1" = "--docbuild" ]; then
 
     # Trac #30002: ensure an English locale so that it is possible to
     # scrape out warnings by pattern matching.
-    # Trac #30576: But we have to avoid the C locale, which disables
-    # proper UTF-8 operation in Python 3.6 or older.
-    LC_ALL=$(locale -a | grep -E -i '^(c|en_us)[-.]utf-?8$' | head -n 1)
-    LANG=$LC_ALL
-    export LC_ALL
-    export LANG
+    export LANG=C
 
     # See #30351: bugs in macOS implementations of openblas/libgopm can cause
     # docbuild to hang if multiple OpenMP threads are allowed.

build/pkgs/python3/spkg-configure.m4

@@ -1,5 +1,5 @@
 SAGE_SPKG_CONFIGURE([python3], [
-   m4_pushdef([MIN_VERSION],               [3.6.0])
+   m4_pushdef([MIN_VERSION],               [3.7.0])
    m4_pushdef([MIN_NONDEPRECATED_VERSION], [3.7.0])
    m4_pushdef([LT_VERSION],                [3.10.0])
    AC_ARG_WITH([python],

src/bin/sage

@@ -955,16 +955,6 @@ fi
 exec-runtests() {
     sage_setup
     export PYTHONIOENCODING="utf-8"  # Fix encoding for doctests
-    # Trac #31191: Some versions of Python 3.6 disable utf-8 even if
-    # the locale is just "POSIX".  This leads to errors in both the
-    # doctest framework and in various individual doctests.
-    if locale | grep -q -E -i '^LC_CTYPE="(C|POSIX)"$'; then
-        # Get an UTF-8 locale if possible.
-        LC_ALL=$(locale -a | grep -E -i '^(c|en_us)[-.]utf-?8$' | head -n 1)
-        LANG=$LC_ALL
-        export LC_ALL
-        export LANG
-    fi
     exec sage-runtests "$@"
 }
 

src/doc/en/installation/source.rst

@@ -178,8 +178,7 @@ rather than building a Python 3 installation from scratch.
 Use the configure option ``--without-system-python3`` in case you want Python 3
 built from scratch.
 
-Sage will accept versions 3.6.x to 3.9.x; however, support for system python 3.6.x
-is deprecated and will be removed in the next development cycle.
+Sage will accept versions 3.7.x to 3.9.x.
 
 You can also use ``--with-python=/path/to/python3_binary`` to tell Sage to use
 ``/path/to/python3_binary`` to set up the venv. Note that setting up venv requires

src/sage/combinat/subset.py

@@ -353,25 +353,20 @@ def cardinality(self):
             8
             sage: Subsets(3).cardinality()
             8
-        """
-        return Integer(1) << self._s.cardinality()
-
-    def __len__(self):
-        r"""
-        Equivalent to ``self.cardinality()``.
 
         TESTS::
 
-            ``__len__`` should return a Python int; in Python 3.7+ this happens
-            automatically, but not on Python 3.6.
+            ``__len__`` should return a Python int.
 
             sage: S = Subsets(Set([1,2,3]))
             sage: len(S)
             8
             sage: type(len(S)) is int
             True
         """
-        return int(self.cardinality())
+        return Integer(1) << self._s.cardinality()
+
+    __len__ = cardinality
 
     def first(self):
         """

src/sage/graphs/views.pyx

@@ -626,7 +626,6 @@ cdef class EdgesView:
         elif i < 0:
             return list(self)[i]
         else:
-            i = int(i)  # For Python < 3.7 where islice doesn't support non-int
             try:
                 return next(islice(self, i, i + 1, 1))
             except StopIteration:

src/setup.cfg.m4

@@ -19,15 +19,14 @@ classifiers =
     Operating System :: POSIX
     Operating System :: MacOS :: MacOS X
     Programming Language :: Python :: 3 :: Only
-    Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: Implementation :: CPython
     Topic :: Scientific/Engineering :: Mathematics
 
 [options]
-python_requires = >=3.6, <3.10
+python_requires = >=3.7, <3.10
 install_requires =
     sage_conf
     esyscmd(`sage-get-system-packages install-requires \

tox.ini

@@ -408,7 +408,6 @@ setenv =
     homebrew-python3.9:       CONFIG_CONFIGURE_ARGS_1=--with-system-python3=force --with-python={env:HOMEBREW}/opt/[email protected]/bin/python3
     # https://github.com/pypa/manylinux
     manylinux-standard:       CONFIG_CONFIGURE_ARGS_1=--with-system-python3=force --with-python=/opt/python/cp38-cp38/bin/python3
-    manylinux-python3.6:      CONFIG_CONFIGURE_ARGS_1=--with-system-python3=force --with-python=/opt/python/cp36-cp36m/bin/python3
     manylinux-python3.7:      CONFIG_CONFIGURE_ARGS_1=--with-system-python3=force --with-python=/opt/python/cp37-cp37m/bin/python3
     manylinux-python3.8:      CONFIG_CONFIGURE_ARGS_1=--with-system-python3=force --with-python=/opt/python/cp38-cp38/bin/python3
     manylinux-python3.9:      CONFIG_CONFIGURE_ARGS_1=--with-system-python3=force --with-python=/opt/python/cp39-cp39/bin/python3