Return a connection pool configured from the given URL.

        For example::

            redis://[:password]@localhost:6379/0
            rediss://[:password]@localhost:6379/0
            unix://[:password]@/path/to/socket.sock?db=0

        Three URL schemes are supported:

        - ```redis://``
          <https://www.iana.org/assignments/uri-schemes/prov/redis>`_ creates a
          normal TCP socket connection
        - ```rediss://``
          <https://www.iana.org/assignments/uri-schemes/prov/rediss>`_ creates
          a SSL wrapped TCP socket connection
        - ``unix://`` creates a Unix Domain Socket connection

        There are several ways to specify a database number. The parse function
        will return the first specified option:
            1. A ``db`` querystring option, e.g. redis://localhost?db=0
            2. If using the redis:// scheme, the path argument of the url, e.g.
               redis://localhost/0
            3. The ``db`` argument to this function.

        If none of these options are specified, db=0 is used.

        The ``decode_components`` argument allows this function to work with
        percent-encoded URLs. If this argument is set to ``True`` all ``%xx``
        escapes will be replaced by their single-character equivalents after
        the URL has been parsed. This only applies to the ``hostname``,
        ``path``, and ``password`` components.

        Any additional querystring arguments and keyword arguments will be
        passed along to the ConnectionPool class's initializer. The querystring
        arguments ``socket_connect_timeout`` and ``socket_timeout`` if supplied
        are parsed as float values. The arguments ``socket_keepalive`` and
        ``retry_on_timeout`` are parsed to boolean values that accept
        True/False, Yes/No values to indicate state. Invalid types cause a
        ``UserWarning`` to be raised. In the case of conflicting arguments,
        querystring arguments always win.

def from_url(cls, url, db=None, decode_components=False, **kwargs):
        """
        Return a connection pool configured from the given URL.

        For example::

            redis://[:password]@localhost:6379/0
            rediss://[:password]@localhost:6379/0
            unix://[:password]@/path/to/socket.sock?db=0

        Three URL schemes are supported:

        - ```redis://``
          <https://www.iana.org/assignments/uri-schemes/prov/redis>`_ creates a
          normal TCP socket connection
        - ```rediss://``
          <https://www.iana.org/assignments/uri-schemes/prov/rediss>`_ creates
          a SSL wrapped TCP socket connection
        - ``unix://`` creates a Unix Domain Socket connection

        There are several ways to specify a database number. The parse function
        will return the first specified option:
            1. A ``db`` querystring option, e.g. redis://localhost?db=0
            2. If using the redis:// scheme, the path argument of the url, e.g.
               redis://localhost/0
            3. The ``db`` argument to this function.

        If none of these options are specified, db=0 is used.

        The ``decode_components`` argument allows this function to work with
        percent-encoded URLs. If this argument is set to ``True`` all ``%xx``
        escapes will be replaced by their single-character equivalents after
        the URL has been parsed. This only applies to the ``hostname``,
        ``path``, and ``password`` components.

        Any additional querystring arguments and keyword arguments will be
        passed along to the ConnectionPool class's initializer. The querystring
        arguments ``socket_connect_timeout`` and ``socket_timeout`` if supplied
        are parsed as float values. The arguments ``socket_keepalive`` and
        ``retry_on_timeout`` are parsed to boolean values that accept
        True/False, Yes/No values to indicate state. Invalid types cause a
        ``UserWarning`` to be raised. In the case of conflicting arguments,
        querystring arguments always win.

        """
        url = urlparse(url)
        url_options = {}

        for name, value in iteritems(parse_qs(url.query)):
            if value and len(value) > 0:
                parser = URL_QUERY_ARGUMENT_PARSERS.get(name)
                if parser:
                    try:
                        url_options[name] = parser(value[0])
                    except (TypeError, ValueError):
                        warnings.warn(UserWarning(
                            "Invalid value for `%s` in connection URL." % name
                        ))
                else:
                    url_options[name] = value[0]

        if decode_components:
            password = unquote(url.password) if url.password else None
            path = unquote(url.path) if url.path else None
            hostname = unquote(url.hostname) if url.hostname else None
        else:
            password = url.password
            path = url.path
            hostname = url.hostname

        # We only support redis://, rediss:// and unix:// schemes.
        if url.scheme == 'unix':
            url_options.update({
                'password': password,
                'path': path,
                'connection_class': UnixDomainSocketConnection,
            })

        elif url.scheme in ('redis', 'rediss'):
            url_options.update({
                'host': hostname,
                'port': int(url.port or 6379),
                'password': password,
            })

            # If there's a path argument, use it as the db argument if a
            # querystring value wasn't specified
            if 'db' not in url_options and path:
                try:
                    url_options['db'] = int(path.replace('/', ''))
                except (AttributeError, ValueError):
                    pass

            if url.scheme == 'rediss':
                url_options['connection_class'] = SSLConnection
        else:
            valid_schemes = ', '.join(('redis://', 'rediss://', 'unix://'))
            raise ValueError('Redis URL must specify one of the following'
                             'schemes (%s)' % valid_schemes)

        # last shot at the db value
        url_options['db'] = int(url_options.get('db', db or 0))

        # update the arguments from the URL values
        kwargs.update(url_options)

        # backwards compatability
        if 'charset' in kwargs:
            warnings.warn(DeprecationWarning(
                '"charset" is deprecated. Use "encoding" instead'))
            kwargs['encoding'] = kwargs.pop('charset')
        if 'errors' in kwargs:
            warnings.warn(DeprecationWarning(
                '"errors" is deprecated. Use "encoding_errors" instead'))
            kwargs['encoding_errors'] = kwargs.pop('errors')

        return cls(**kwargs)