py3: switched to python38 by default.

default.nix

@@ -6,7 +6,7 b''
 
 args@
 { system ? builtins.currentSystem
-, pythonPackages ? "python37Packages"
+, pythonPackages ? "python38Packages"
 , pythonExternalOverrides ? self: super: {}
 , doCheck ? false
 , ...

pkgs/overlays.nix

@@ -46,7 +46,7 b' self: super: {'
   #  - activate special python bindings
   subversionrc =
   let
-    py3c = self.python37Packages.buildPythonPackage rec {
+    py3c = self.python38Packages.buildPythonPackage rec {
         pname = "py3c";
         version = "1.0";
         src = self.fetchurl {
@@ -65,7 +65,7 b' self: super: {'
     };
   in
   let
-    pythonWithEnv = self.python37Packages.python.buildEnv.override {
+    pythonWithEnv = self.python38Packages.python.buildEnv.override {
         extraLibs = [ py3c ];
     };
   in

pkgs/python-packages.nix

@@ -536,9 +536,7 b' self: super: {'
       self."setuptools-scm"
       self."wheel"
     ];
-    propagatedBuildInputs = [
-      self."importlib-metadata"
-    ];
+    propagatedBuildInputs = [];
     meta = {
       license = [ pkgs.lib.licenses.mit ];
     };
@@ -700,7 +698,6 b' self: super: {'
     propagatedBuildInputs = [
       self."atomicwrites"
       self."attrs"
-      self."importlib-metadata"
       self."more-itertools"
       self."packaging"
       self."pluggy"

pkgs/shell-generate.nix

@@ -1,5 +1,5 b''
 { pkgs ? (import <nixpkgs> {})
-, pythonPackages ? "python37Packages"
+, pythonPackages ? "python38Packages"
 }:
 
 with pkgs.lib;

shell.nix

@@ -2,7 +2,7 b''
 # environment.
 
 { pkgs ? (import <nixpkgs> {})
-, pythonPackages ? "python37Packages"
+, pythonPackages ? "python38Packages"
 , doCheck ? false
 }: