Make default flux unit DN; bump minimum Python req

Author: ojustino

setup.cfg

@@ -14,7 +14,7 @@ github_project = astropy/specreduce
 [options]
 zip_safe = False
 packages = find:
-python_requires = >=3.7
+python_requires = >=3.8
 setup_requires = setuptools_scm
 install_requires =
     astropy

specreduce/core.py

@@ -70,7 +70,7 @@ def _parse_image(self, image, disp_axis=1):
         else:
             uncertainty = VarianceUncertainty(np.ones(img.shape))
 
-        unit = getattr(image, 'unit', u.Unit('DN'))  # or u.Unit()?
+        unit = getattr(image, 'unit', u.Unit('DN'))
 
         spectral_axis = getattr(image, 'spectral_axis',
                                 np.arange(img.shape[disp_axis]) * u.pix)

specreduce/extract.py

@@ -258,7 +258,7 @@ class HorneExtract(SpecreduceOperation):
     unit : `~astropy.units.Unit` or str, optional
         (Only used if ``image`` is not an NDData object.)
         The associated unit for the data in ``image``. If blank,
-        fluxes are interpreted as unitless. [default: None]
+        fluxes are interpreted in DN. [default: None]
 
     """
     image: NDData
@@ -307,7 +307,7 @@ def _parse_image(self, image,
         unit : `~astropy.units.Unit` or str, optional
             (Only used if ``image`` is not an NDData object.)
             The associated unit for the data in ``image``. If blank,
-            fluxes are interpreted as unitless.
+            fluxes are interpreted in DN.
         disp_axis : int, optional
             The index of the image's dispersion axis. Should not be
             changed until operations can handle variable image
@@ -381,7 +381,7 @@ def _parse_image(self, image,
         variance = VarianceUncertainty(variance)
 
         unit = getattr(image, 'unit',
-                       u.Unit(unit) if unit is not None else u.Unit())
+                       u.Unit(unit) if unit is not None else u.Unit('DN'))
 
         spectral_axis = getattr(image, 'spectral_axis',
                                 np.arange(img.shape[disp_axis]) * u.pix)
@@ -434,7 +434,7 @@ def __call__(self, image=None, trace_object=None,
         unit : `~astropy.units.Unit` or str, optional
             (Only used if ``image`` is not an NDData object.)
             The associated unit for the data in ``image``. If blank,
-            fluxes are interpreted as unitless.
+            fluxes are interpreted in DN.
 
 
         Returns

specreduce/tests/test_extract.py

@@ -116,10 +116,10 @@ def test_horne_image_validation():
         ext = extract(image=image.data, variance=err, mask=mask)
 
     # an array-type image given without mask and unit arguments is fine
-    # and produces an extraction with unitless flux and spectral axis in pixels
+    # and produces an extraction with flux in DN and spectral axis in pixels
     err = np.ones_like(image)
     ext = extract(image=image.data, variance=err, mask=None, unit=None)
-    assert ext.unit == u.Unit()
+    assert ext.unit == u.Unit('DN')
     assert np.all(ext.spectral_axis
                   == np.arange(image.shape[extract.disp_axis]) * u.pix)