Use an explicit class instance for simbad queries

Importing Simbad and using what looks like a module/class
methods actually instantiates a secret object, and causes
all sorts of problems, so never do that.

spectractor/extractor/targets.py

@@ -1,6 +1,7 @@
 from astropy.coordinates import SkyCoord, Distance
 import astropy.units as u
 from astropy.time import Time
+from astroquery.simbad import SimbadClass
 
 import matplotlib.pyplot as plt
 from scipy.interpolate import interp1d
@@ -194,7 +195,6 @@ def __init__(self, label, verbose=False):
         """
         Target.__init__(self, label, verbose=verbose)
         self.my_logger = set_logger(self.__class__.__name__)
-        self.simbad = None
         self.load()
 
     def load(self):
@@ -212,28 +212,31 @@ def load(self):
         >>> print(s.radec_position.dec)
         -66d02m22.635s
         """
-        # currently (pending a new release) astroquery has a race
-        # condition at import time, so putting here rather than at the
-        # module level so that multiple test runners don't run the race
-        from astroquery.simbad import Simbad
-        patchSimbadURL(Simbad)
-        Simbad.add_votable_fields('flux(U)', 'flux(B)', 'flux(V)', 'flux(R)', 'flux(I)', 'flux(J)', 'sptype',
-                                  'parallax', 'pm', 'z_value')
+        # explicitly make a class instance here because:
+        # when using ``from astroquery.simbad import Simbad`` and then using
+        # ``Simbad...`` methods secretly makes an instance, which stays around,
+        # has a connection go stale, and then raises an exception seemingly
+        # at some random time later
+        simbadQuerier = SimbadClass()
+        patchSimbadURL(simbadQuerier)
+
+        simbadQuerier.add_votable_fields('flux(U)', 'flux(B)', 'flux(V)', 'flux(R)', 'flux(I)', 'flux(J)', 'sptype',
+                                         'parallax', 'pm', 'z_value')
         astroquery_label = self.label
         if getCalspec.is_calspec(self.label):
             calspec = getCalspec.Calspec(self.label)
             astroquery_label = calspec.Astroquery_Name
-        simbad = Simbad.query_object(astroquery_label)
-        self.simbad = simbad
-        if simbad is not None:
+        simbad_table = simbadQuerier.query_object(astroquery_label)
+
+        if simbad_table is not None:
             if self.verbose or True:
-                self.my_logger.info(f'\n\tSimbad:\n{simbad}')
-            self.radec_position = SkyCoord(simbad['RA'][0] + ' ' + simbad['DEC'][0], unit=(u.hourangle, u.deg))
+                self.my_logger.info(f'\n\tSimbad:\n{simbad_table}')
+            self.radec_position = SkyCoord(simbad_table['RA'][0] + ' ' + simbad_table['DEC'][0], unit=(u.hourangle, u.deg))
         else:
-            self.my_logger.warning(f'Target {self.label} not found in Simbad')
-        self.get_radec_position_after_pm(date_obs="J2000")
-        if not np.ma.is_masked(simbad['Z_VALUE']):
-            self.redshift = float(simbad['Z_VALUE'])
+            raise RuntimeError(f"Target {self.label} not found in Simbad")
+        self.get_radec_position_after_pm(simbad_table, date_obs="J2000")
+        if not np.ma.is_masked(simbad_table['Z_VALUE']):
+            self.redshift = float(simbad_table['Z_VALUE'])
         else:
             self.redshift = 0
         self.load_spectra()
@@ -335,14 +338,14 @@ def load_spectra(self):
                              f"\n\tEmission spectrum ? {self.emission_spectrum}"
                              f"\n\tLines: {[l.label for l in self.lines.lines]}")
 
-    def get_radec_position_after_pm(self, date_obs):
-        target_pmra = self.simbad[0]['PMRA'] * u.mas / u.yr
+    def get_radec_position_after_pm(self, simbad_table, date_obs):
+        target_pmra = simbad_table[0]['PMRA'] * u.mas / u.yr
         if np.isnan(target_pmra):
             target_pmra = 0 * u.mas / u.yr
-        target_pmdec = self.simbad[0]['PMDEC'] * u.mas / u.yr
+        target_pmdec = simbad_table[0]['PMDEC'] * u.mas / u.yr
         if np.isnan(target_pmdec):
             target_pmdec = 0 * u.mas / u.yr
-        target_parallax = self.simbad[0]['PLX_VALUE'] * u.mas
+        target_parallax = simbad_table[0]['PLX_VALUE'] * u.mas
         if target_parallax == 0 * u.mas:
             target_parallax = 1e-4 * u.mas
         target_coord = SkyCoord(ra=self.radec_position.ra, dec=self.radec_position.dec,