add deprecation warning BPIC and DIC (pymc-devs#2754)

* add deprecation warning BPIC and DIC

* fix typo

* do not hide warning messages

Author: aloctavodia

RELEASE-NOTES.md

@@ -15,6 +15,7 @@
 - Michael Osthege added support for population-samplers and implemented differential evolution metropolis (`DEMetropolis`).  For models with correlated dimensions that can not use gradient-based samplers, the `DEMetropolis` sampler can give higher effective sampling rates. (also see [PR#2735](https://github.com/pymc-devs/pymc3/pull/2735))
 - Forestplot supports multiple traces (#2736)
 - Add new plot, densityplot (#2741)
+- DIC and BPIC calculations have been deprecated
 
 ### Fixes
 

docs/source/notebooks/GLM-model-selection.ipynb

@@ -116,6 +116,9 @@ def dic(trace, model=None):
     z : float
         The deviance information criterion of the model and trace
     """
+    warnings.warn("dic has been deprecated. Use `waic` or `loo` instead.", DeprecationWarning,
+                  stacklevel=2)
+
     model = modelcontext(model)
     logp = model.logp
 
@@ -464,6 +467,9 @@ def bpic(trace, model=None):
     z : float
         The Bayesian predictive information criterion of the model and trace
     """
+    warnings.warn("bpic has been deprecated. Use `waic` or `loo` instead.", DeprecationWarning,
+                  stacklevel=2)
+
     model = modelcontext(model)
     logp = model.logp
 
@@ -1005,7 +1011,7 @@ def summary(trace, varnames=None, transform=lambda x: x, stat_funcs=None,
 
 def df_summary(*args, **kwargs):
     warnings.warn("df_summary has been deprecated. In future, use summary instead.",
-                DeprecationWarning)
+                  DeprecationWarning, stacklevel=2)
     return summary(*args, **kwargs)