fix how derives are imported when reading output (#320)

previously, if the solver itself did not define derives.py, then
we didn't add any derived variables.  But compressible uses a lot
of inheritance, and only the base compressible has derives.py.
Now we loop over the inheritance hierarchy and try importing
derives until we find it.

Also add machnumber to the compressible derives

Author: zingale

pyro/compressible/derives.py

@@ -57,6 +57,9 @@ def derive_primitives(myd, varnames):
         elif var == "soundspeed":
             derived_vars.append(np.sqrt(gamma*p/dens))
 
+        elif var == "machnumber":
+            derived_vars.append(np.sqrt(u**2 + v**2) / np.sqrt(gamma*p/dens))
+
         elif var == "vorticity":
             derived_vars.append(vort)
 

pyro/util/io_pyro.py

@@ -127,13 +127,20 @@ def read(filename):
 
             sim.read_extras(f)
 
-        # check if there are derived variables
-        try:
-            derives = importlib.import_module(f"pyro.{solver_name}.derives")
-            sim.cc_data.add_derived(derives.derive_primitives)
-
-        except ModuleNotFoundError:
-            pass
+            # check if there are derived variables -- since we do a lot of
+            # inheritance, we want to start with the deepest class and
+            # work backwards through the inheritance until we find a derives
+            # module
+            for mod in [cls.__module__ for cls in type(sim).__mro__ if cls is not object]:
+                try:
+                    derives = importlib.import_module(f"{mod.replace('simulation', 'derives')}")
+                    sim.cc_data.add_derived(derives.derive_primitives)
+
+                except ModuleNotFoundError:
+                    continue
+
+                else:
+                    break
 
     if solver_name is not None:
         return sim