Merge pull request #296 from bgilbert/chaining

Include all `LoadLibrary()` failures in exception chain

openslide/__init__.py

@@ -293,8 +293,8 @@ def set_cache(self, cache: OpenSlideCache) -> None:
         cache: an OpenSlideCache object."""
         try:
             llcache = cache._openslide_cache
-        except AttributeError:
-            raise TypeError('Not a cache object')
+        except AttributeError as exc:
+            raise TypeError('Not a cache object') from exc
         lowlevel.set_cache(self._osr, llcache)
 
 

openslide/lowlevel.py

@@ -72,30 +72,32 @@ def _load_library() -> CDLL:
         pass
 
     def try_load(names: list[str]) -> CDLL:
-        for name in names:
-            try:
-                return cdll.LoadLibrary(name)
-            except OSError:
-                if name == names[-1]:
-                    raise
-        else:
-            raise ValueError('No library names specified')
+        try:
+            return cdll.LoadLibrary(names[0])
+        except OSError:
+            remaining = names[1:]
+            if remaining:
+                # handle recursively so implicit exception chaining captures
+                # all the failures
+                return try_load(remaining)
+            else:
+                raise
 
     if platform.system() == 'Windows':
         try:
             return try_load(['libopenslide-1.dll', 'libopenslide-0.dll'])
-        except FileNotFoundError:
+        except FileNotFoundError as exc:
             raise ModuleNotFoundError(
                 "Couldn't locate OpenSlide DLL. "
                 "Try `pip install openslide-bin`, "
                 "or if you're using an OpenSlide binary package, "
                 "ensure you've called os.add_dll_directory(). "
                 "https://openslide.org/api/python/#installing"
-            )
+            ) from exc
     elif platform.system() == 'Darwin':
         try:
             return try_load(['libopenslide.1.dylib', 'libopenslide.0.dylib'])
-        except OSError:
+        except OSError as exc:
             # MacPorts doesn't add itself to the dyld search path, but
             # does add itself to the find_library() search path
             # (DEFAULT_LIBRARY_FALLBACK in ctypes.macholib.dyld).
@@ -107,17 +109,17 @@ def try_load(names: list[str]) -> CDLL:
                     "Couldn't locate OpenSlide dylib. "
                     "Try `pip install openslide-bin`. "
                     "https://openslide.org/api/python/#installing"
-                )
+                ) from exc
             return cdll.LoadLibrary(lib)
     else:
         try:
             return try_load(['libopenslide.so.1', 'libopenslide.so.0'])
-        except OSError:
+        except OSError as exc:
             raise ModuleNotFoundError(
                 "Couldn't locate OpenSlide shared library. "
                 "Try `pip install openslide-bin`. "
                 "https://openslide.org/api/python/#installing"
-            )
+            ) from exc
 
 
 _lib = _load_library()