Made sample_shape same across all contexts, thereby resolves pymc-devs#3758

Author: Sayam753

pymc3/distributions/distribution.py

@@ -690,6 +690,7 @@ def draw_values(params, point=None, size=None):
     """
     # The following check intercepts and redirects calls to
     # draw_values in the context of sample_posterior_predictive
+    size = to_tuple(size)
     ppc_sampler = vectorized_ppc.get(None)
     if ppc_sampler is not None:
         # this is being done inside new, vectorized sample_posterior_predictive

pymc3/tests/test_distributions_random.py

@@ -1664,6 +1664,10 @@ def test_issue_3758(self):
         for var in "abcd":
             assert not np.isnan(np.std(samples[var]))
 
+        for var in "bcd":
+            std = np.std(samples[var] - samples["a"])
+            np.testing.assert_allclose(std, 1, rtol=1e-2)
+
     def test_issue_3829(self):
         with pm.Model() as model:
             x = pm.MvNormal("x", mu=np.zeros(5), cov=np.eye(5), shape=(2, 5))