lowlevel: add attribute indicating whether a function is available

Add `available` attribute on lowlevel functions to indicate whether
OpenSlide supports the function, without the need to call it.  Update
tests to use this; drop maybe_supported decorator.

Signed-off-by: Benjamin Gilbert <bgilbert@cs.cmu.edu>

Author: bgilbert

openslide/lowlevel.py

@@ -263,14 +263,28 @@ def _func(name, restype, argtypes, errcheck=_check_error, minimum_version=None):
         def function_unavailable(*_args):
             raise OpenSlideVersionError(minimum_version)
 
+        # allow checking for availability without calling the function
+        function_unavailable.available = False
+
         return function_unavailable
     func.argtypes = argtypes
     func.restype = restype
     if errcheck is not None:
         func.errcheck = errcheck
+    func.available = True
     return func
 
 
+def _wraps_funcs(wrapped):
+    def decorator(f):
+        f.available = True
+        for w in wrapped:
+            f.available = f.available and w.available
+        return f
+
+    return decorator
+
+
 try:
     detect_vendor = _func('openslide_detect_vendor', c_char_p, [_utf8_p], _check_string)
 except AttributeError:
@@ -289,6 +303,7 @@ def function_unavailable(*_args):
 )
 
 
+@_wraps_funcs([_get_level_dimensions])
 def get_level_dimensions(slide, level):
     w, h = c_int64(), c_int64()
     _get_level_dimensions(slide, level, byref(w), byref(h))
@@ -310,6 +325,7 @@ def get_level_dimensions(slide, level):
 )
 
 
+@_wraps_funcs([_read_region])
 def read_region(slide, x, y, level, w, h):
     if w < 0 or h < 0:
         # OpenSlide would catch this, but not before we tried to allocate
@@ -349,6 +365,7 @@ def read_region(slide, x, y, level, w, h):
 )
 
 
+@_wraps_funcs([_get_associated_image_dimensions])
 def get_associated_image_dimensions(slide, name):
     w, h = c_int64(), c_int64()
     _get_associated_image_dimensions(slide, name, byref(w), byref(h))
@@ -360,6 +377,7 @@ def get_associated_image_dimensions(slide, name):
 )
 
 
+@_wraps_funcs([get_associated_image_dimensions, _read_associated_image])
 def read_associated_image(slide, name):
     w, h = get_associated_image_dimensions(slide, name)
     buf = (w * h * c_uint32)()

tests/common.py

@@ -17,7 +17,6 @@
 # Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 #
 
-from functools import wraps
 import os
 from pathlib import Path
 
@@ -41,22 +40,6 @@
 
             os.environ['PATH'] = _orig_path
 
-from openslide import OpenSlideVersionError
-
 
 def file_path(name):
     return Path(__file__).parent / 'fixtures' / name
-
-
-def maybe_supported(f):
-    '''Decorator to ignore test failures caused by an OpenSlide version that
-    doesn't support the tested functionality.'''
-
-    @wraps(f)
-    def wrapper(*args, **kwargs):
-        try:
-            return f(*args, **kwargs)
-        except OpenSlideVersionError:
-            pass
-
-    return wrapper

tests/test_base.py

@@ -1,7 +1,7 @@
 #
 # openslide-python - Python bindings for the OpenSlide library
 #
-# Copyright (c) 2016 Benjamin Gilbert
+# Copyright (c) 2016-2023 Benjamin Gilbert
 #
 # This library is free software; you can redistribute it and/or modify it
 # under the terms of version 2.1 of the GNU Lesser General Public License
@@ -17,11 +17,12 @@
 # Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 #
 
+import ctypes
 import unittest
 
 from common import file_path
 
-from openslide import ImageSlide, OpenSlide, open_slide
+from openslide import ImageSlide, OpenSlide, lowlevel, open_slide
 
 
 class TestLibrary(unittest.TestCase):
@@ -30,3 +31,17 @@ def test_open_slide(self):
             self.assertTrue(isinstance(osr, OpenSlide))
         with open_slide(file_path('boxes.png')) as osr:
             self.assertTrue(isinstance(osr, ImageSlide))
+
+    def test_lowlevel_available(self):
+        '''Ensure all exported functions have an 'available' attribute.'''
+        for name in dir(lowlevel):
+            # ignore classes and unexported functions
+            if name.startswith('_') or name[0].isupper():
+                continue
+            # ignore random imports
+            if hasattr(ctypes, name) or name in ('count', 'platform'):
+                continue
+            self.assertTrue(
+                hasattr(getattr(lowlevel, name), 'available'),
+                f'"{name}" missing "available" attribute',
+            )

tests/test_imageslide.py

@@ -1,7 +1,7 @@
 #
 # openslide-python - Python bindings for the OpenSlide library
 #
-# Copyright (c) 2016-2021 Benjamin Gilbert
+# Copyright (c) 2016-2023 Benjamin Gilbert
 #
 # This library is free software; you can redistribute it and/or modify it
 # under the terms of version 2.1 of the GNU Lesser General Public License
@@ -20,9 +20,9 @@
 import unittest
 
 from PIL import Image
-from common import file_path, maybe_supported
+from common import file_path
 
-from openslide import ImageSlide, OpenSlideCache, OpenSlideError
+from openslide import ImageSlide, OpenSlideCache, OpenSlideError, lowlevel
 
 
 class TestImageWithoutOpening(unittest.TestCase):
@@ -105,7 +105,7 @@ def test_read_region_bad_size(self):
     def test_thumbnail(self):
         self.assertEqual(self.osr.get_thumbnail((100, 100)).size, (100, 83))
 
-    @maybe_supported
+    @unittest.skipUnless(lowlevel.cache_create.available, "requires OpenSlide 4.0.0")
     def test_set_cache(self):
         self.osr.set_cache(OpenSlideCache(64 << 10))
         self.assertEqual(self.osr.read_region((0, 0), 0, (400, 400)).size, (400, 400))

tests/test_openslide.py

@@ -1,7 +1,7 @@
 #
 # openslide-python - Python bindings for the OpenSlide library
 #
-# Copyright (c) 2016-2021 Benjamin Gilbert
+# Copyright (c) 2016-2023 Benjamin Gilbert
 #
 # This library is free software; you can redistribute it and/or modify it
 # under the terms of version 2.1 of the GNU Lesser General Public License
@@ -23,18 +23,19 @@
 import unittest
 
 from PIL import Image
-from common import file_path, maybe_supported
+from common import file_path
 
 from openslide import (
     OpenSlide,
     OpenSlideCache,
     OpenSlideError,
     OpenSlideUnsupportedFormatError,
+    lowlevel,
 )
 
 
 class TestCache(unittest.TestCase):
-    @maybe_supported
+    @unittest.skipUnless(lowlevel.cache_create.available, "requires OpenSlide 4.0.0")
     def test_create_cache(self):
         OpenSlideCache(0)
         OpenSlideCache(1)
@@ -155,7 +156,7 @@ def _test_read_region_2GB(self):
     def test_thumbnail(self):
         self.assertEqual(self.osr.get_thumbnail((100, 100)).size, (100, 83))
 
-    @maybe_supported
+    @unittest.skipUnless(lowlevel.cache_create.available, "requires OpenSlide 4.0.0")
     def test_set_cache(self):
         self.osr.set_cache(OpenSlideCache(64 << 10))
         self.assertEqual(self.osr.read_region((0, 0), 0, (400, 400)).size, (400, 400))