def is_response_to_head(response):
    """
    Checks whether the request of a response has been a HEAD-request.
    Handles the quirks of AppEngine.

    :param http.client.HTTPResponse response:
        Response to check if the originating request
        used 'HEAD' as a method.
    """
    # FIXME: Can we do this somehow without accessing private httplib _method?
    method = response._method
    if isinstance(method, int):  # Platform-specific: Appengine
        return method == 3
    return method.upper() == "HEAD"

    Checks whether the request of a response has been a HEAD-request.
    Handles the quirks of AppEngine.

    :param http.client.HTTPResponse response:
        Response to check if the originating request
        used 'HEAD' as a method.
    
lib/urllib3/util/response.py