python::pip hangs with ensure "latest" behind a proxy server

[mmanzato-athesis]

I'm behind a http proxy. This one:

python::pip {
    "numpy":
        ensure     => 'latest',
        proxy      => 'http://my.proxy:3128';
}

apparently hangs the update since it runs pip search with no --proxy argument. I've found that adding {$proxy_flag} argument to pip search solves the issue.