Add a _has_dataset method to Ion (#270)

fiasco/ions.py

@@ -143,6 +143,17 @@ def _instance_kwargs(self):
             kwargs['abundance'] = self.abundance
         return kwargs
 
+    def _has_dataset(self, dset_name):
+        # There are some cases where we need to check for the existence of a dataset
+        # within a function as opposed to checking for the existence of that dataset
+        # before entering the function using the decorator approach.
+        try:
+            needs_dataset(dset_name)(lambda _: None)(self)
+        except MissingDatasetException:
+            return False
+        else:
+            return True
+
     def next_ion(self):
         """
         Return an `~fiasco.Ion` instance with the next highest ionization stage.
@@ -1409,13 +1420,7 @@ def free_bound(self,
         wavelength = np.atleast_1d(wavelength)
         prefactor = (2/np.sqrt(2*np.pi)/(const.h*(const.c**3) * (const.m_e * const.k_B)**(3/2)))
         recombining = self.next_ion()
-        try:
-            # NOTE: This checks whether the fblvl data is available for the
-            # recombining ion
-            needs_dataset('fblvl')(lambda _: None)(recombining)
-            omega_0 = recombining._fblvl['multiplicity'][0]
-        except MissingDatasetException:
-            omega_0 = 1.0
+        omega_0 = recombining._fblvl['multiplicity'][0] if recombining._has_dataset('fblvl') else 1.0
         E_photon = const.h * const.c / wavelength
         energy_temperature_factor = np.outer(self.temperature**(-3/2), E_photon**5)
         # Fill in observed energies with theoretical energies

fiasco/tests/test_ion.py

@@ -423,3 +423,12 @@ def test_new_instance_abundance_preserved_string(ion):
     new_ion = ion._new_instance()
     assert u.allclose(new_ion.abundance, 2.818382931264455e-05)
     assert new_ion._dset_names['abundance'] == 'sun_photospheric_2007_grevesse'
+
+
+def test_has_dataset(ion, c6):
+    # Fe 5 has energy level data
+    assert ion._has_dataset('elvlc')
+    # Fe 5 has no proton data
+    assert not ion._has_dataset('psplups')
+    # C VI has no dielectronic data
+    assert not c6._has_dataset('dielectronic_elvlc')