Make ASDF extension robust to missing asdf-astropy

CHANGES.rst

@@ -24,7 +24,7 @@ New Features
 ^^^^^^^^^^^^
 
 - Added an ASDF extension to provide converters for photutils aperture
-  and PSF classes. [#2211]
+  and PSF classes. [#2211, #2268]
 
 Bug Fixes
 ^^^^^^^^^

photutils/converters/__init__.py

@@ -1,20 +1,20 @@
 # Licensed under a 3-clause BSD style license - see LICENSE.rst
 """
-ASDF converters.
+ASDF converters for photutils objects.
+
+``CircularApertureConverter`` requires only ``asdf``.  ``AiryDiskPSFConverter``
+requires ``asdf-astropy`` for full functionality; it is always registered but
+raises a clear ``ImportError`` when ``asdf-astropy`` is not installed.
 """
 
-_ASDF_ASTROPY_INSTALLED = True
+from .apertures import CircularApertureConverter  # noqa: F401
+from .functional_models import AiryDiskPSFConverter  # noqa: F401
 
 try:
-    import asdf_astropy  # noqa: F401 -- needed to register the converters
+    import asdf_astropy  # noqa: F401 -- only used to detect availability
 except ImportError:
     _ASDF_ASTROPY_INSTALLED = False
+else:
+    _ASDF_ASTROPY_INSTALLED = True
 
-if _ASDF_ASTROPY_INSTALLED:
-    from .functional_models import AiryDiskPSFConverter
-    from .apertures import CircularApertureConverter
-
-__all__ = [
-    'AiryDiskPSFConverter',
-    'CircularApertureConverter',
-]
+__all__ = ['AiryDiskPSFConverter', 'CircularApertureConverter']

photutils/converters/functional_models.py

@@ -3,13 +3,15 @@
 Converters to and from the ASDF format for photutils.psf.functional_models.
 """
 
-from . import _ASDF_ASTROPY_INSTALLED
-
-if _ASDF_ASTROPY_INSTALLED:
+try:
     from asdf_astropy.converters.transform.core import (TransformConverterBase,
                                                         parameter_to_value)
-else:
-    TransformConverterBase = object
+
+    _ASDF_ASTROPY_AVAILABLE = True
+except ImportError:
+    from asdf.extension import Converter as TransformConverterBase
+
+    _ASDF_ASTROPY_AVAILABLE = False
 
 __all__ = ['AiryDiskPSFConverter']
 
@@ -22,22 +24,39 @@ class AiryDiskPSFConverter(TransformConverterBase):
     tags = ('tag:astropy.org:photutils/psf/airy_disk_psf-*',)
     types = ('photutils.psf.AiryDiskPSF',)
 
-    def to_yaml_tree_transform(self, model, tag, ctx):  # noqa: ARG002
-        return {
-            'flux': parameter_to_value(model.flux),
-            'x_0': parameter_to_value(model.x_0),
-            'y_0': parameter_to_value(model.y_0),
-            'radius': parameter_to_value(model.radius),
-            'bbox_factor': model.bbox_factor,
-        }
-
-    def from_yaml_tree_transform(self, node, tag, ctx):  # noqa: ARG002
-        from photutils.psf import AiryDiskPSF
-
-        return AiryDiskPSF(
-            flux=node['flux'],
-            x_0=node['x_0'],
-            y_0=node['y_0'],
-            radius=node['radius'],
-            bbox_factor=node['bbox_factor'],
-        )
+    if _ASDF_ASTROPY_AVAILABLE:
+        def to_yaml_tree_transform(self, model, tag, ctx):  # noqa: ARG002
+            return {
+                'flux': parameter_to_value(model.flux),
+                'x_0': parameter_to_value(model.x_0),
+                'y_0': parameter_to_value(model.y_0),
+                'radius': parameter_to_value(model.radius),
+                'bbox_factor': model.bbox_factor,
+            }
+
+        def from_yaml_tree_transform(self, node, tag, ctx):  # noqa: ARG002
+            from photutils.psf import AiryDiskPSF
+
+            return AiryDiskPSF(
+                flux=node['flux'],
+                x_0=node['x_0'],
+                y_0=node['y_0'],
+                radius=node['radius'],
+                bbox_factor=node['bbox_factor'],
+            )
+    else:
+        def to_yaml_tree(self, obj, tag, ctx):  # noqa: ARG002
+            msg = (
+                'asdf-astropy must be installed to serialize AiryDiskPSF '
+                'to ASDF format. Install it with:\n'
+                '    pip install asdf-astropy'
+            )
+            raise ImportError(msg)
+
+        def from_yaml_tree(self, node, tag, ctx):  # noqa: ARG002
+            msg = (
+                'asdf-astropy must be installed to deserialize AiryDiskPSF '
+                'from ASDF format. Install it with:\n'
+                '    pip install asdf-astropy'
+            )
+            raise ImportError(msg)

photutils/converters/tests/test_apertures.py

@@ -8,16 +8,13 @@
 import pytest
 
 from photutils.aperture import CircularAperture
-from photutils.converters import _ASDF_ASTROPY_INSTALLED
 
 apertures = [
     CircularAperture(positions=[(1, 2), (3, 4)], r=5),
     CircularAperture(positions=(5, 6), r=7),
 ]
 
 
-@pytest.mark.skipif(not _ASDF_ASTROPY_INSTALLED,
-                    reason='asdf-astropy is not installed')
 @pytest.mark.parametrize('aperture', apertures)
 def test_aperture_converters(tmp_path, aperture):
     """

photutils/converters/tests/test_psf.py

@@ -26,3 +26,35 @@ def test_psf_converters(tmp_path, airy_disk_psf):
             for parameter in pars:
                 assert_array_equal(getattr(psf, parameter),
                                    getattr(psf2, parameter))
+
+
+@pytest.mark.skipif(_ASDF_ASTROPY_INSTALLED,
+                    reason='asdf-astropy is installed; error not expected')
+def test_airy_disk_psf_serialize_no_asdf_astropy(tmp_path):
+    """
+    Test that serializing AiryDiskPSF without asdf-astropy raises a
+    friendly ImportError.
+    """
+    from photutils.psf import AiryDiskPSF
+
+    psf = AiryDiskPSF(flux=1, x_0=0, y_0=0, radius=5)
+    with asdf.AsdfFile() as af:
+        af['psf'] = psf
+        with pytest.raises(ImportError,
+                           match='asdf-astropy must be installed'):
+            af.write_to(tmp_path / 'psf.asdf')
+
+
+@pytest.mark.skipif(_ASDF_ASTROPY_INSTALLED,
+                    reason='asdf-astropy is installed; error not expected')
+def test_airy_disk_psf_deserialize_no_asdf_astropy():
+    """
+    Test that deserializing AiryDiskPSF without asdf-astropy raises a
+    friendly ImportError.
+    """
+    from photutils.converters.functional_models import AiryDiskPSFConverter
+
+    converter = AiryDiskPSFConverter()
+    with pytest.raises(ImportError,
+                       match='asdf-astropy must be installed'):
+        converter.from_yaml_tree({}, None, None)

photutils/extension.py

@@ -8,24 +8,23 @@
 from asdf.extension import ManifestExtension
 from asdf.resource import DirectoryResourceMapping
 
-from .converters import apertures  # import CircularApertureConverter
-from .converters import functional_models  # import AiryDiskPSFConverter
+from .converters import apertures, functional_models
 
 __all__ = [
     'PHOTUTILS_APERTURE_CONVERTERS',
+    'PHOTUTILS_CONVERTERS',
     'PHOTUTILS_MANIFEST_URIS',
     'PHOTUTILS_PSF_CONVERTERS',
 ]
 
-PHOTUTILS_PSF_CONVERTERS = [
-    functional_models.AiryDiskPSFConverter(),
-]
-
 PHOTUTILS_APERTURE_CONVERTERS = [
     apertures.CircularApertureConverter(),
 ]
+PHOTUTILS_PSF_CONVERTERS = [
+    functional_models.AiryDiskPSFConverter(),
+]
 
-PHOTUTILS_CONVERTERS = PHOTUTILS_PSF_CONVERTERS + PHOTUTILS_APERTURE_CONVERTERS
+PHOTUTILS_CONVERTERS = PHOTUTILS_APERTURE_CONVERTERS + PHOTUTILS_PSF_CONVERTERS
 
 # The order here is important; asdf will prefer to use extensions
 # that occur earlier in the list.