Better handling of variable names in e.g. GraphViz graphs (#4403)

* handle changed API of theano.gof.graph.stack_search

* convert n and eta to tensors, explicitly list parameters for repr

* improve robustness of get_repr_for_variable

* Revert "handle changed API of theano.gof.graph.stack_search"

This reverts commit 6238bff.

pymc3/distributions/multivariate.py

@@ -963,8 +963,8 @@ class _LKJCholeskyCov(Continuous):
     """
 
     def __init__(self, eta, n, sd_dist, *args, **kwargs):
-        self.n = n
-        self.eta = eta
+        self.n = tt.as_tensor_variable(n)
+        self.eta = tt.as_tensor_variable(eta)
 
         if "transform" in kwargs and kwargs["transform"] is not None:
             raise ValueError("Invalid parameter: transform.")
@@ -1129,6 +1129,9 @@ def random(self, point=None, size=None):
             samples = np.reshape(samples, size + sample_shape)
         return samples
 
+    def _distr_parameters_for_repr(self):
+        return ["eta", "n"]
+
 
 def LKJCholeskyCov(name, eta, n, sd_dist, compute_corr=False, store_in_trace=True, *args, **kwargs):
     R"""Wrapper function for covariance matrix with LKJ distributed correlations.

pymc3/util.py

@@ -131,7 +131,13 @@ def get_default_varnames(var_iterator, include_transformed):
 
 def get_repr_for_variable(variable, formatting="plain"):
     """Build a human-readable string representation for a variable."""
-    name = variable.name if variable is not None else None
+    if variable is not None and hasattr(variable, "name"):
+        name = variable.name
+    elif type(variable) in [float, int, str]:
+        name = str(variable)
+    else:
+        name = None
+
     if name is None and variable is not None:
         if hasattr(variable, "get_parents"):
             try: