From 5cab1f7a4c147b6079583582231b021e5a837d7a Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Thu, 27 Jan 2022 13:57:09 -0500
Subject: [PATCH] Get Python this way?

---
 .circleci/config.yml |  2 +-
 .circleci/python.nix | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)
 create mode 100644 .circleci/python.nix

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 9d9b967f1..e4d6c9e93 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -458,7 +458,7 @@ jobs:
           name: "Generation version"
           command: |
             # The Nix package doesn't know how to do this part, unfortunately.
-            nix-shell -p python --run 'python setup.py update_version'
+            nix-shell .circleci/python.nix --run 'python setup.py update_version'
 
       - "run":
           name: "Build and Test"
diff --git a/.circleci/python.nix b/.circleci/python.nix
new file mode 100644
index 000000000..a830ee61b
--- /dev/null
+++ b/.circleci/python.nix
@@ -0,0 +1,11 @@
+# Define a helper environment for incidental Python tasks required on CI.
+let
+  sources = import ../nix/sources.nix;
+in
+{ pkgs ? import sources."nixpkgs-21.11" { }
+}:
+pkgs.mkShell {
+  buildInputs = [
+    pkgs.python3
+  ];
+}