python3Minimal: Add top-level for a minimal Python 3 build

This builds Python without optional dependencies.

We can't just use python3.override, as things like
python3Minimal.withPackages would pass the wrong python derivation into
these modules.

pkgs/development/interpreters/python/default.nix

@@ -111,6 +111,38 @@ in {
     inherit passthruFun;
   };
 
+  # Minimal versions of Python (built without optional dependencies)
+  python3Minimal = (callPackage ./cpython {
+    self = python3Minimal;
+    sourceVersion = {
+      major = "3";
+      minor = "7";
+      patch = "4";
+      suffix = "";
+    };
+    sha256 = "0gxiv5617zd7dnqm5k9r4q2188lk327nf9jznwq9j6b8p0s92ygv";
+    inherit (darwin) CF configd;
+    inherit passthruFun;
+
+    # strip down that python version as much as possible
+    openssl = null;
+    readline = null;
+    ncurses = null;
+    gdbm = null;
+    sqlite = null;
+    stripConfig = true;
+    stripIdlelib = true;
+    stripTests = true;
+    stripTkinter = true;
+    rebuildBytecode = false;
+    stripBytecode = true;
+  }).overrideAttrs(old: {
+    pname = "python3-minimal";
+    meta = old.meta // {
+      maintainers = [];
+    };
+  });
+
   pypy27 = callPackage ./pypy {
     self = pypy27;
     sourceVersion = {

pkgs/top-level/all-packages.nix

@@ -8754,7 +8754,7 @@ in
   python3Packages = python3.pkgs;
 
   pythonInterpreters = callPackage ./../development/interpreters/python {};
-  inherit (pythonInterpreters) python27 python35 python36 python37 python38 pypy27 pypy36;
+  inherit (pythonInterpreters) python27 python35 python36 python37 python38 python3Minimal pypy27 pypy36;
 
   # Python package sets.
   python27Packages = lib.hiPrioSet (recurseIntoAttrs python27.pkgs);