Add support for astropy registry priorities

specutils/io/registers.py

@@ -1,6 +1,7 @@
 """
 A module containing the mechanics of the specutils io registry.
 """
+import inspect
 import os
 import pathlib
 import sys
@@ -16,6 +17,16 @@
 log = logging.getLogger(__name__)
 
 
+def _astropy_has_priorities():
+    """
+    Check if astropy has support for loader priorities
+    """
+    sig = inspect.signature(io_registry.register_reader)
+    if sig.parameters.get("priority") is not None:
+        return True
+    return False
+
+
 def data_loader(label, identifier=None, dtype=Spectrum1D, extensions=None,
                 priority=0):
     """
@@ -52,7 +63,10 @@ def wrapper(*args, **kwargs):
         return wrapper
 
     def decorator(func):
-        io_registry.register_reader(label, dtype, func)
+        if _astropy_has_priorities():
+            io_registry.register_reader(label, dtype, func, priority=priority)
+        else:
+            io_registry.register_reader(label, dtype, func)
 
         if identifier is None:
             # If the identifier is not defined, but the extensions are, create
@@ -78,17 +92,6 @@ def decorator(func):
         # Include the file extensions as attributes on the function object
         func.extensions = extensions
 
-        # Include priority on the loader function attribute
-        func.priority = priority
-
-        # Sort the io_registry based on priority
-        sorted_loaders = sorted(io_registry._readers.items(),
-                                key=lambda item: getattr(item[1], 'priority', 0))
-
-        # Update the registry with the sorted dictionary
-        io_registry._readers.clear()
-        io_registry._readers.update(sorted_loaders)
-
         log.debug("Successfully loaded reader \"{}\".".format(label))
 
         # Automatically register a SpectrumList reader for any data_loader that
@@ -102,7 +105,14 @@ def load_spectrum_list(*args, **kwargs):
             load_spectrum_list.extensions = extensions
             load_spectrum_list.priority = priority
 
-            io_registry.register_reader(label, SpectrumList, load_spectrum_list)
+            if _astropy_has_priorities():
+                io_registry.register_reader(
+                    label, SpectrumList, load_spectrum_list, priority=priority,
+                )
+            else:
+                io_registry.register_reader(
+                    label, SpectrumList, load_spectrum_list,
+                )
             io_registry.register_identifier(label, SpectrumList, id_func)
             log.debug("Created SpectrumList reader for \"{}\".".format(label))
 
@@ -113,9 +123,12 @@ def wrapper(*args, **kwargs):
     return decorator
 
 
-def custom_writer(label, dtype=Spectrum1D):
+def custom_writer(label, dtype=Spectrum1D, priority=0):
     def decorator(func):
-        io_registry.register_writer(label, Spectrum1D, func)
+        if _astropy_has_priorities():
+            io_registry.register_writer(label, dtype, func, priority=priority)
+        else:
+            io_registry.register_writer(label, dtype, func)
 
         @wraps(func)
         def wrapper(*args, **kwargs):

specutils/tests/test_io.py

@@ -4,6 +4,7 @@
 This module tests SpecUtils io routines
 """
 
+from collections import Counter
 from specutils.io.parsing_utils import generic_spectrum_from_table # or something like that
 from astropy.io import registry
 from astropy.table import Table
@@ -15,7 +16,8 @@
 import warnings
 
 from specutils import Spectrum1D, SpectrumList
-from specutils.io import data_loader
+from specutils.io import data_loader, custom_writer
+from specutils.io.registers import _astropy_has_priorities
 
 
 def test_generic_spectrum_from_table(recwarn):
@@ -156,3 +158,48 @@ def reader(*args, **kwargs):
         # Clean up after ourselves
         registry.unregister_reader(format_name, datatype)
         registry.unregister_identifier(format_name, datatype)
+
+
+@pytest.mark.xfail(
+    not _astropy_has_priorities(),
+    reason="Test requires priorities to be implemented in astropy",
+    raises=registry.IORegistryError,
+)
+def test_loader_uses_priority(tmpdir):
+    counter = Counter()
+    fname = str(tmpdir.join('good.txt'))
+
+    with open(fname, 'w') as ff:
+        ff.write('\n')
+
+    def identifier(origin, *args, **kwargs):
+        fname = args[0]
+        return 'good' in fname
+
+    @data_loader("test_counting_loader1", identifier=identifier, priority=1)
+    def counting_loader1(*args, **kwargs):
+        counter["test1"] += 1
+        wave = np.arange(1,1.1,0.01)*u.AA
+        return Spectrum1D(
+            spectral_axis=wave,
+            flux=np.ones(len(wave))*1.e-14*u.Jy,
+        )
+
+    @data_loader("test_counting_loader2", identifier=identifier, priority=2)
+    def counting_loader2(*args, **kwargs):
+        counter["test2"] += 1
+        wave = np.arange(1,1.1,0.01)*u.AA
+        return Spectrum1D(
+            spectral_axis=wave,
+            flux=np.ones(len(wave))*1.e-14*u.Jy,
+        )
+
+    Spectrum1D.read(fname)
+    assert counter["test2"] == 1
+    assert counter["test1"] == 0
+
+    for datatype in [Spectrum1D, SpectrumList]:
+        registry.unregister_reader("test_counting_loader1", datatype)
+        registry.unregister_identifier("test_counting_loader1", datatype)
+        registry.unregister_reader("test_counting_loader2", datatype)
+        registry.unregister_identifier("test_counting_loader2", datatype)