python3 is now python37 instead of python36

With Python 3.7 now at 3.7.1, and Python 3.6 at it's final maintenance
mode release, it is time to move on to 3.7 as the default interpreter.

doc/languages-frameworks/python.section.md

@@ -484,9 +484,9 @@ and in this case the `python35` interpreter is automatically used.
 ### Interpreters
 
 Versions 2.7, 3.4, 3.5, 3.6 and 3.7 of the CPython interpreter are available as
-respectively `python27`, `python34`, `python35` and `python36`. The PyPy interpreter
+respectively `python27`, `python34`, `python35`, `python36` and `python37`. The PyPy interpreter
 is available as `pypy`. The aliases `python2` and `python3` correspond to respectively `python27` and
-`python35`. The default interpreter, `python`, maps to `python2`.
+`python37`. The default interpreter, `python`, maps to `python2`.
 The Nix expressions for the interpreters can be found in
 `pkgs/development/interpreters/python`.
 
@@ -538,7 +538,7 @@ sets are
 and the aliases
 
 * `pkgs.python2Packages` pointing to `pkgs.python27Packages`
-* `pkgs.python3Packages` pointing to `pkgs.python36Packages`
+* `pkgs.python3Packages` pointing to `pkgs.python37Packages`
 * `pkgs.pythonPackages` pointing to `pkgs.python2Packages`
 
 #### `buildPythonPackage` function

nixos/doc/manual/release-notes/rl-1903.xml

@@ -19,6 +19,8 @@
 
   <itemizedlist>
    <listitem>
+    <para>
+    The default Python 3 interpreter is now CPython 3.7 instead of CPython 3.6.
     <para />
    </listitem>
   </itemizedlist>

pkgs/top-level/all-packages.nix

@@ -7756,7 +7756,7 @@ with pkgs;
   # When switching these sets, please update docs at ../../doc/languages-frameworks/python.md
   python = python2;
   python2 = python27;
-  python3 = python36;
+  python3 = python37;
   pypy = pypy27;
 
   # Python interpreter that is build with all modules, including tkinter.
@@ -7806,8 +7806,8 @@ with pkgs;
   python27Packages = lib.hiPrioSet (recurseIntoAttrs python27.pkgs);
   python34Packages = python34.pkgs;
   python35Packages = python35.pkgs;
-  python36Packages = recurseIntoAttrs python36.pkgs;
-  python37Packages = python37.pkgs;
+  python36Packages = python36.pkgs;
+  python37Packages = recurseIntoAttrs python37.pkgs;
   pypyPackages = pypy.pkgs;
 
   # Should eventually be moved inside Python interpreters.