infinite recursion

nix eval --show-trace '(with import <nixpkgs> { overlays = [ import ./overlays.nix ]; }; python27Packages )'
error: while evaluating anonymous function at /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/top-level/impure.nix:15:1, called from (string):1:7:
while evaluating anonymous function at /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/top-level/default.nix:20:1, called from /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/top-level/impure.nix:82:1:
while evaluating anonymous function at /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/stdenv/booter.nix:42:1, called from /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/top-level/default.nix:108:10:
while evaluating 'dfold' at /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/stdenv/booter.nix:60:27, called from /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/stdenv/booter.nix:117:4:
while evaluating 'go' at /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/stdenv/booter.nix:63:18, called from /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/stdenv/booter.nix:72:13:
while evaluating 'folder' at /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/stdenv/booter.nix:89:33, called from /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/stdenv/booter.nix:68:18:
while evaluating 'allPackages' at /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/top-level/default.nix:98:17, called from /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/stdenv/booter.nix:101:10:
while evaluating anonymous function at /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/top-level/stage.nix:12:1, called from /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/top-level/default.nix:98:26:
while evaluating 'fix' at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/fixed-points.nix:19:9, called from /nix/var/nix/profiles/per-user/root/channels/nixos/pkgs/top-level/stage.nix:221:3:
while evaluating 'extends' at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/fixed-points.nix:66:24, called from /nix/var/nix/profiles/per-user/root/channels/nixos/lib/fixed-points.nix:19:20:
while evaluating 'extends' at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/fixed-points.nix:66:24, called from /nix/var/nix/profiles/per-user/root/channels/nixos/lib/fixed-points.nix:66:42:
while evaluating 'extends' at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/fixed-points.nix:66:24, called from /nix/var/nix/profiles/per-user/root/channels/nixos/lib/fixed-points.nix:66:42:
infinite recursion encountered, at undefined position

overlays.nix

self: super: {
  python = super.python.override {
    packageOverrides = python-self: python-super: {
      # # new tahoe-lafs dependency
      # eliot = python-self.callPackage ./eliot.nix { };
      # # new autobahn requires a newer cryptography
      # cryptography = python-self.callPackage ./cryptography.nix { };
      # # new tahoe-lafs depends on a very recent autobahn for better
      # # websocket testing features.
      # autobahn = python-self.callPackage ./autobahn.nix { };

      # # tahoe-lafs in nixpkgs is packaged as an application!  so we have to
      # # re-package it ourselves as a library.
      # tahoe-lafs = python-self.callPackage ./tahoe-lafs.nix { };
    };
  };
}