Please change this line to:
```ruby
system python, "setup.py", "install", "--prefix=#{prefix}"
```

The python must not be quoted, since it is a Homebrew object pointing to the python binary, but you can also call certain methods, e.g. `python.site_packages` (not needed here).

If you get an error that the dir is not in the `PYTHONPATH`, then use this instead (it will set it up for you and create the dir):
```ruby
def install
  python do
    system python, "setup.py", "install", "--prefix=#{prefix}"
  end
end
```

Some (older) setup.py scripts want to install and link an easy-install.pth file. That is bad and in this case you'll have to pass two additional args to setup.py: `--single-version-externally-managed` and `--record=installed.txt`.