anchor.diff:      sqlalchemy
       sqlalchemy-continuum
       werkzeug
  -    wtforms
  +    pinned_wtforms
       psycopg2
       debts
     ];
  
positive.code: { buildPythonPackage, lib, fetchFromGitHub, isPy27, nixosTests, fetchpatch
  , alembic
  , aniso8601
  , Babel
  
negative.code: , psycopg2 # optional, for postgresql support
  , flask_testing
  }:
  
  # ihatemoney is not really a library. It will only ever be imported
  # by the interpreter of uwsgi. So overrides for its depencies are fine.
  let
    # https://github.com/spiral-project/ihatemoney/issues/567
    pinned_wtforms = wtforms.overridePythonAttrs (old: rec {
      pname = "WTForms";
      version = "2.2.1";
      src = fetchPypi {
        inherit pname version;
        sha256 = "0q9vkcq6jnnn618h27lx9sas6s9qlg2mv8ja6dn0hy38gwzarnqc";
      };
    });
    pinned_flask_wtf = flask_wtf.override { wtforms = pinned_wtforms; };
  in
  
  buildPythonPackage rec {
    pname = "ihatemoney";
  