python3: now points to python38

Note this also means python3Minimal is now also Python 3.8.

This reverts commit eb1369670b and adds more.

doc/languages-frameworks/python.section.md

@@ -643,7 +643,7 @@ and in this case the `python38` interpreter is automatically used.
 Versions 2.7, 3.5, 3.6, 3.7 and 3.8 of the CPython interpreter are available as
 respectively `python27`, `python35`, `python36`, `python37` and `python38`. The
 aliases `python2` and `python3` correspond to respectively `python27` and
-`python37`. The default interpreter, `python`, maps to `python2`. The PyPy
+`python38`. The default interpreter, `python`, maps to `python2`. The PyPy
 interpreters compatible with Python 2.7 and 3 are available as `pypy27` and
 `pypy3`, with aliases `pypy2` mapping to `pypy27` and `pypy` mapping to `pypy2`.
 The Nix expressions for the interpreters can be found in

nixos/doc/manual/release-notes/rl-2009.xml

@@ -42,6 +42,11 @@
      PHP now defaults to PHP 7.4, updated from 7.3.
     </para>
    </listitem>
+   <listitem>
+    <para>
+     Python 3 now defaults to Python 3.8 instead of 3.7.
+    </para>
+   </listitem>
    <listitem>
     <para>
      Two new options, <link linkend="opt-services.openssh.authorizedKeysCommand">authorizedKeysCommand</link>

pkgs/development/interpreters/python/default.nix

@@ -129,7 +129,7 @@ in {
   };
 
   # Minimal versions of Python (built without optional dependencies)
-  python3Minimal = (python37.override {
+  python3Minimal = (python3.override {
     self = python3Minimal;
     pythonForBuild = pkgs.buildPackages.python3Minimal;
     # strip down that python version as much as possible

pkgs/top-level/all-packages.nix

@@ -9646,7 +9646,7 @@ in
   # When switching these sets, please update docs at ../../doc/languages-frameworks/python.md
   python = python2;
   python2 = python27;
-  python3 = python37;
+  python3 = python38;
   pypy = pypy2;
   pypy2 = pypy27;
   pypy3 = pypy36;