Improve error message when a stanvariable is not found

Author: WardBrian

cmdstanpy/stanfit/mcmc.py

@@ -619,7 +619,7 @@ def draws_xr(
 
     def stan_variable(
         self,
-        var: Optional[str] = None,
+        var: str,
         inc_warmup: bool = False,
     ) -> np.ndarray:
         """
@@ -660,10 +660,12 @@ def stan_variable(
         CmdStanVB.stan_variable
         CmdStanGQ.stan_variable
         """
-        if var is None:
-            raise ValueError('No variable name specified.')
         if var not in self._metadata.stan_vars_dims:
-            raise ValueError('Unknown variable name: {}'.format(var))
+            raise ValueError(
+                f'Unknown variable name: {var}\n'
+                'Available variables are '
+                + ", ".join(self._metadata.stan_vars_dims)
+            )
         if self._draws.shape == (0,):
             self._assemble_draws()
         draw1 = 0
@@ -1130,7 +1132,7 @@ def draws_xr(
 
     def stan_variable(
         self,
-        var: Optional[str] = None,
+        var: str,
         inc_warmup: bool = False,
     ) -> np.ndarray:
         """
@@ -1171,12 +1173,14 @@ def stan_variable(
         CmdStanMLE.stan_variable
         CmdStanVB.stan_variable
         """
-        if var is None:
-            raise ValueError('No variable name specified.')
         model_var_names = self.mcmc_sample.metadata.stan_vars_cols.keys()
         gq_var_names = self.metadata.stan_vars_cols.keys()
         if not (var in model_var_names or var in gq_var_names):
-            raise ValueError('Unknown variable name: {}'.format(var))
+            raise ValueError(
+                f'Unknown variable name: {var}\n'
+                'Available variables are '
+                + ", ".join(model_var_names | gq_var_names)
+            )
         if var not in gq_var_names:
             return self.mcmc_sample.stan_variable(var, inc_warmup=inc_warmup)
         else:  # is gq variable

cmdstanpy/stanfit/mle.py

@@ -155,7 +155,7 @@ def optimized_params_dict(self) -> Dict[str, float]:
 
     def stan_variable(
         self,
-        var: Optional[str] = None,
+        var: str,
         *,
         inc_iterations: bool = False,
         warn: bool = True,
@@ -179,10 +179,12 @@ def stan_variable(
         CmdStanVB.stan_variable
         CmdStanGQ.stan_variable
         """
-        if var is None:
-            raise ValueError('no variable name specified.')
         if var not in self._metadata.stan_vars_dims:
-            raise ValueError('unknown variable name: {}'.format(var))
+            raise ValueError(
+                f'Unknown variable name: {var}\n'
+                'Available variables are '
+                + ", ".join(self._metadata.stan_vars_dims)
+            )
         if warn and inc_iterations and not self._save_iterations:
             get_logger().warning(
                 'Intermediate iterations not saved to CSV output file. '

cmdstanpy/stanfit/vb.py

@@ -103,9 +103,7 @@ def metadata(self) -> InferenceMetadata:
         """
         return self._metadata
 
-    def stan_variable(
-        self, var: Optional[str] = None
-    ) -> Union[np.ndarray, float]:
+    def stan_variable(self, var: str) -> Union[np.ndarray, float]:
         """
         Return a numpy.ndarray which contains the estimates for the
         for the named Stan program variable where the dimensions of the
@@ -123,7 +121,11 @@ def stan_variable(
         if var is None:
             raise ValueError('No variable name specified.')
         if var not in self._metadata.stan_vars_dims:
-            raise ValueError('Unknown variable name: {}'.format(var))
+            raise ValueError(
+                f'Unknown variable name: {var}\n'
+                'Available variables are '
+                + ", ".join(self._metadata.stan_vars_dims)
+            )
         col_idxs = list(self._metadata.stan_vars_cols[var])
         shape: Tuple[int, ...] = ()
         if len(col_idxs) > 1: