fix bug in io_pymc3 and add warning for PyMC3<3.9 (#1203)

* fix bug in io_pymc3 and add warning for PyMC3<3.9 * update changelog
arviz-devs · May 23, 2020 · f1db2c4 · f1db2c4
1 parent 8676e40
commit f1db2c4
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### New features
 
 ### Maintenance and fixes
+* fix bug in `from_pymc3` when used with PyMC3<3.9 (#1203)
 
 ### Deprecation
 

diff --git a/arviz/data/io_pymc3.py b/arviz/data/io_pymc3.py
@@ -105,7 +105,13 @@ def __init__(
                     "tuning_steps": trace.report.n_tune,
                 }
             else:
-                self.nchains = len(trace)
+                self.ndraws = len(trace)
+                if self.save_warmup:
+                    warnings.warn(
+                        "Warmup samples will be stored in posterior group and will not be"
+                        " excluded from stats and diagnostics. Please consider using PyMC3>=3.9",
+                        UserWarning,
+                    )
         else:
             self.nchains = self.ndraws = 0