upgrade to Python 3.9

ltfatpy/sigproc/firkaiser.py

@@ -152,7 +152,7 @@ def firkaiser(L, beta, centering='wp', norm='null'):
         # the data to complex, otherwise np.sqrt returns nan
         tmp = k*(L-1.-k)
         tmp = tmp.astype('complex128')
-        k = 2. * beta / (L-1) * np.sqrt(tmp)
+        k = np.real(2. * beta / (L-1) * np.sqrt(tmp))
         g = np.i0(k) / np.i0(beta)
 
     g = np.fft.ifftshift(g)

ltfatpy/tests/comp/test_comp_gabdual.py

@@ -84,10 +84,15 @@ class TestCompGabDual(unittest.TestCase):
             assertRaisesRegex = self.assertRaisesRegex
         except AttributeError:
             assertRaisesRegex = self.assertRaisesRegexp
+
+        # I checked that the command comp_gabdual_long(g, 0, 0) raises a
+        # TypeError with the correct message -- Still complaining with NULL
+        # being returned
         assertRaisesRegex(TypeError, mess, comp_gabdual_long, g, 0, 0)
         g = g.astype(np.float64)
         # g dim should be < 3
         mess = "g dimensions should be 1 or 2."
+        # Same as above -- Is that a change of behaviour of assertRaisesRegex?
         assertRaisesRegex(
             TypeError, mess, comp_gabdual_long, g.reshape((3, 1, 3)), 0, 0)
         # basic test: