def normalise_toolshed_url(tool_shed):
    """
    Return complete URL for a tool shed

    Arguments:
      tool_shed (str): partial or full URL for a
        toolshed server

    Returns:
      str: full URL for toolshed, including
        leading protocol.

    """
    if tool_shed.startswith('http://') or \
       tool_shed.startswith('https://'):
        return tool_shed
    return "https://%s" % tool_shed