human
Solve the following python programming problem given the following code:
def MockRequest(env, **kwargs) : 
    "Request object for testing. Keyword arguments populate an
    `environ` dictionary and the callbacks.

    If `authname` is specified in a keyword arguments a `PermissionCache`
    object is created, otherwise if `authname` is not specified or is
    `None` a `MockPerm` object is used and the `authname` is set to
    'anonymous'.

    The following keyword arguments are commonly used:
    :keyword args: dictionary of request arguments
    :keyword authname: the name of the authenticated user, or 'anonymous'
    :keyword method: the HTTP request method
    :keyword path_info: the request path inside the application

    Additionally `format`, `locale`, `lc_time`, `remote_addr`,
    `remote_user`, `script_name`, `server_name`, `server_port`
    and `tz` can be specified as keyword arguments.

    :since: 1.0.11
    " 
    authname = kwargs.get ('authname') 
    if (authname is None) : 
        authname = 'anonymous' 
        perm = MockPerm () 
else : 
        perm = PermissionCache (env, authname) 
args = _RequestArgs () 
    args.update (kwargs.get ('args', { 
        
})) 
    environ = { 
        'trac.base_url' : env.abs_href (), 
        'wsgi.url_scheme' : 'http', 
        'HTTP_ACCEPT_LANGUAGE' : 'en-US', 
        'PATH_INFO' : kwargs.get ('path_info', '/'), 
        'REQUEST_METHOD' : kwargs.get ('method', 'GET'), 
        'REMOTE_ADDR' : kwargs.get ('remote_addr', '127.0.0.1'), 
        'REMOTE_USER' : kwargs.get ('remote_user', authname), 
        'SCRIPT_NAME' : kwargs.get ('script_name', '/trac.cgi'), 
        'SERVER_NAME' : kwargs.get ('server_name', 'localhost'), 
        'SERVER_PORT' : kwargs.get ('server_port', '80'), 
} 
    status_sent = [] 
    headers_sent = { 
        
} 
    response_sent = StringIO.StringIO () 
    def start_response(status, headers, exc_info = None) : 
        status_sent.append (status) 
        headers_sent.update (dict (headers)) 
        return response_sent.write 
req = Mock (Request, environ, start_response) 
   ...

    
    

    Fix the buggy line: req.headers_sent = authname
assistant
#Here is Python code to fix the buggy line: req.

req.headers_sent = headers_sent