Merge pull request #2281 from aseyboldt/discrete-trafo

Disallow transformations for discrete variables

Author: Junpeng Lao

pymc3/distributions/distribution.py

@@ -87,7 +87,7 @@ def getattr_value(self, val):
 
     def _repr_latex_(self, name=None, dist=None):
         return None
-                                                                     
+
 
 def TensorType(dtype, shape):
     return tt.TensorType(str(dtype), np.atleast_1d(shape) == 1)
@@ -123,6 +123,11 @@ def __init__(self, shape=(), dtype=None, defaults=('mode', ),
                 dtype = 'int64'
         if dtype != 'int16' and dtype != 'int64':
             raise TypeError('Discrete classes expect dtype to be int16 or int64.')
+
+        if kwargs.get('transform', None) is not None:
+            raise ValueError("Transformations for discrete distributions "
+                             "are not allowed.")
+
         super(Discrete, self).__init__(
             shape, dtype, defaults=defaults, *args, **kwargs)
 

pymc3/tests/test_distributions.py

@@ -860,3 +860,13 @@ def test_repr_latex_():
     assert x2._repr_latex_()=='$Timeseries \\sim \\text{GaussianRandomWalk}(\\mathit{mu}=Continuous, \\mathit{sd}=1.0)$'
     assert x3._repr_latex_()=='$Multivariate \\sim \\text{MvStudentT}(\\mathit{nu}=5, \\mathit{mu}=Timeseries, \\mathit{Sigma}=array)$'
     assert x4._repr_latex_()=='$Mixture \\sim \\text{NormalMixture}(\\mathit{w}=array, \\mathit{mu}=Multivariate, \\mathit{sigma}=f(Discrete))$'
+
+
+def test_discrete_trafo():
+    with pytest.raises(ValueError) as err:
+        Binomial.dist(n=5, p=0.5, transform='log')
+    err.match('Transformations for discrete distributions')
+    with Model():
+        with pytest.raises(ValueError) as err:
+            Binomial('a', n=5, p=0.5, transform='log')
+        err.match('Transformations for discrete distributions')