Add a type guard for intX

RELEASE-NOTES.md

@@ -19,6 +19,7 @@
 - `pm.make_shared_replacements` now retains broadcasting information which fixes issues with Metropolis samplers (see [#4492](https://github.com/pymc-devs/pymc3/pull/4492)).
 
 **Release manager** for 3.11.2: Michael Osthege ([@michaelosthege](https://github.com/michaelosthege))
+- `pm.intX` did bad job with downcasting integers. It is fixed in [#4569](https://github.com/pymc-devs/pymc3/pull/4569).
 
 ## PyMC3 3.11.1 (12 February 2021)
 

pymc3/tests/test_data_container.py

@@ -78,7 +78,7 @@ def test_sample_posterior_predictive_after_set_data(self):
             trace = pm.sample(1000, tune=1000, chains=1)
         # Predict on new data.
         with model:
-            x_test = [5, 6, 9]
+            x_test = [5.0, 6.0, 9.0]
             pm.set_data(new_data={"x": x_test})
             y_test = pm.sample_posterior_predictive(trace)
             y_test1 = pm.fast_sample_posterior_predictive(trace)

pymc3/tests/test_model_helpers.py

@@ -82,7 +82,7 @@ def test_pandas_to_array(self, input_dtype):
         assert isinstance(theano_output, theano.graph.basic.Variable)
         npt.assert_allclose(theano_output.eval(), theano_graph_input.eval())
         intX = pm.theanof._conversion_map[theano.config.floatX]
-        if dense_input.dtype == intX or dense_input.dtype == theano.config.floatX:
+        if "int" in str(dense_input.dtype) or dense_input.dtype == theano.config.floatX:
             assert theano_output.owner is None  # func should not have added new nodes
             assert theano_output.name == input_name
         else:
@@ -92,7 +92,8 @@ def test_pandas_to_array(self, input_dtype):
         if "float" in input_dtype:
             assert theano_output.dtype == theano.config.floatX
         else:
-            assert theano_output.dtype == intX
+            # only cast floats, leave ints as is
+            assert theano_output.dtype == input_dtype
 
         # Check function behavior with generator data
         generator_output = func(square_generator)

pymc3/theanof.py

@@ -93,6 +93,9 @@ def intX(X):
     """
     Convert a theano tensor or numpy array to theano.tensor.int32 type.
     """
+    # check value is already int, do nothing in this case
+    if (hasattr(X, "dtype") and "int" in str(X.dtype)) or isinstance(X, int):
+        return X
     intX = _conversion_map[theano.config.floatX]
     try:
         return X.astype(intX)