':return: The name of the variables which are of file type'

def get_file_vars(self):

    file_keys = set()
    for (k, v_lst) in self.meta.iteritems():
        for v in v_lst:
            if isinstance(v, FileFormField):
                file_keys.add(k)
    for (k, v_lst) in self.items():
        for v in v_lst:
            if is_file_like(v):
                file_keys.add(k)
    return list(file_keys)
