How to use the bambi.backends.base.BackEnd function in bambi

from arviz import from_pymc3
import theano
import pymc3 as pm
from bambi.priors import Prior

from .base import BackEnd


class PyMC3BackEnd(BackEnd):

    """
    PyMC3 model-fitting back-end.
    """

    # Available link functions
    links = {
        "identity": lambda x: x,
        "logit": theano.tensor.nnet.sigmoid,
        "inverse": theano.tensor.inv,
        "inverse_squared": lambda x: theano.tensor.inv(theano.tensor.sqrt(x)),
        "log": theano.tensor.exp,
    }

    dists = {"HalfFlat": pm.Bound(pm.Flat, lower=0)}

import re

import numpy as np
from arviz import from_pystan
from bambi.priors import Prior

from .base import BackEnd

try:
    import pystan as ps
except ImportError:
    ps = None


class StanBackEnd(BackEnd):  # pylint: disable=too-many-instance-attributes

    """
    Stan/PyStan model-fitting back-end.
    """

    # distribution names and arg names should match those in priors.json,
    dists = {
        "Normal": {"name": "normal", "args": ["#mu", "#sd"]},
        "Bernoulli": {"name": "bernoulli", "args": ["#p"]},
        "Poisson": {"name": "poisson", "args": ["#mu"]},
        "Cauchy": {"name": "cauchy", "args": ["#alpha", "#beta"]},
        "HalfNormal": {"name": "normal", "args": ["0", "#sd"], "bounds": ""},
        "HalfCauchy": {"name": "cauchy", "args": ["0", "#beta"], "bounds": ""},
        # for Uniform, the bounds are the parameters. _map_dist fills these in
        "Uniform": {
            "name": "uniform",