start porting inferencedata conversion code

Author: OriolAbril

README.rst

@@ -15,18 +15,6 @@ Check out the `getting started guide <http://docs.pymc.io/notebooks/getting_star
 using Binder!
 For questions on PyMC3, head on over to our `PyMC Discourse <https://discourse.pymc.io/>`__ forum.
 
-The future of PyMC3 & Theano
-============================
-
-There have been many questions and uncertainty around the future of PyMC3 since Theano
-stopped getting developed by the original authors, and we started experiments with PyMC4.
-
-We are happy to announce that PyMC3 on Theano (which we are `developing further <https://github.com/pymc-devs/Theano-PyMC>`__)
-with a new JAX backend is the future. PyMC4 will not be developed further.
-
-See the `full announcement <https://pymc-devs.medium.com/the-future-of-pymc3-or-theano-is-dead-long-live-theano-d8005f8a0e9b>`__
-for more details.
-
 Features
 ========
 

pymc3/__init__.py

@@ -40,7 +40,12 @@ def __set_compiler_flags():
 
 from pymc3 import gp, ode, sampling
 from pymc3.aesaraf import *
-from pymc3.backends import load_trace, save_trace
+from pymc3.backends import (
+    load_trace,
+    predictions_to_inference_data,
+    save_trace,
+    to_inference_data,
+)
 from pymc3.backends.tracetab import *
 from pymc3.blocking import *
 from pymc3.data import *

pymc3/backends/__init__.py

@@ -60,6 +60,7 @@
 Saved backends can be loaded using `arviz.from_netcdf`
 
 """
+from pymc3.backends.arviz import predictions_to_inference_data, to_inference_data
 from pymc3.backends.ndarray import (
     NDArray,
     load_trace,