element, and the local port to the second element. If ``0`` is used as the
    port number, a semi-random high port will be selected.

    .. warning:: Setting an explicit local port can have negative interactions
                 with connection-pooling in Requests: in particular, it risks
                 the possibility of getting "Address in use" errors. The
                 string-only argument is generally preferred to the tuple-form.

    Example usage:

    .. code-block:: python

        import requests
        from requests_toolbelt.adapters.source import SourceAddressAdapter

        s = requests.Session()
        s.mount('http://', SourceAddressAdapter('10.10.10.10'))
        s.mount('https://', SourceAddressAdapter(('10.10.10.10', 8999))
    c