Matplotlib python 2 error

err.txt

these derivations will be built:
  /nix/store/wq0hjy52lvb2065zd9kz28lcm5wjcz27-python-2.7.18-env.drv
building '/nix/store/wq0hjy52lvb2065zd9kz28lcm5wjcz27-python-2.7.18-env.drv'...
collision between `/nix/store/j3h77q52zpkyawh792ldq4p98wzrl2a0-python2.7-backports.ssl_match_hostname-3.7.0.1/lib/python2.7/site-packages/backports/__init__.py' and `/nix/store/xib7gvd0nfknb0skzh8zh3v0rx7bvcvw-python2.7-backports.functools_lru_cache-1.6.1/lib/python2.7/site-packages/backports/__init__.py'
builder for '/nix/store/wq0hjy52lvb2065zd9kz28lcm5wjcz27-python-2.7.18-env.drv' failed with exit code 25
error: build of '/nix/store/wq0hjy52lvb2065zd9kz28lcm5wjcz27-python-2.7.18-env.drv' failed

shell.nix

with import <nixpkgs> {};

let
  deps = packages: [
    packages.matplotlib
  ];
in

pkgs.mkShell {
  buildInputs = [
    (pkgs.python27.withPackages deps)
  ];
}