def clean_id(post_id):
    """
    Fixes the Reddit ID so that it can be used to get a new object.

    By default, the Reddit ID is prefixed with something like `t1_` or
    `t3_`, but this doesn't always work for getting a new object. This
    method removes those prefixes and returns the rest.

    :param post_id: String. Post fullname (ID)
    :return: String. Post fullname minus the first three characters.
    """
    return post_id[post_id.index('_') + 1:]