Small fixes

openslide/__init__.py

@@ -23,8 +23,10 @@
 This package provides Python bindings for the OpenSlide library.
 """
 
+from abc import ABCMeta, abstractmethod
 from collections.abc import Mapping
 from io import BytesIO
+import os
 
 from PIL import Image, ImageCms
 
@@ -53,7 +55,7 @@
 PROPERTY_NAME_BOUNDS_HEIGHT = 'openslide.bounds-height'
 
 
-class AbstractSlide:
+class AbstractSlide(metaclass=ABCMeta):
     """The base class of a slide object."""
 
     def __init__(self):
@@ -67,22 +69,26 @@ def __exit__(self, exc_type, exc_val, exc_tb):
         return False
 
     @classmethod
+    @abstractmethod
     def detect_format(cls, filename):
         """Return a string describing the format of the specified file.
 
         If the file format is not recognized, return None."""
         raise NotImplementedError
 
+    @abstractmethod
     def close(self):
         """Close the slide."""
         raise NotImplementedError
 
     @property
+    @abstractmethod
     def level_count(self):
         """The number of levels in the image."""
         raise NotImplementedError
 
     @property
+    @abstractmethod
     def level_dimensions(self):
         """A list of (width, height) tuples, one for each level of the image.
 
@@ -95,20 +101,23 @@ def dimensions(self):
         return self.level_dimensions[0]
 
     @property
+    @abstractmethod
     def level_downsamples(self):
         """A list of downsampling factors for each level of the image.
 
         level_downsample[n] contains the downsample factor of level n."""
         raise NotImplementedError
 
     @property
+    @abstractmethod
     def properties(self):
         """Metadata about the image.
 
         This is a map: property name -> property value."""
         raise NotImplementedError
 
     @property
+    @abstractmethod
     def associated_images(self):
         """Images associated with this whole-slide image.
 
@@ -122,10 +131,12 @@ def color_profile(self):
             return None
         return ImageCms.getOpenProfile(BytesIO(self._profile))
 
+    @abstractmethod
     def get_best_level_for_downsample(self, downsample):
         """Return the best level for displaying the given downsample."""
         raise NotImplementedError
 
+    @abstractmethod
     def read_region(self, location, level, size):
         """Return a PIL.Image containing the contents of the region.
 
@@ -135,6 +146,7 @@ def read_region(self, location, level, size):
         size:     (width, height) tuple giving the region size."""
         raise NotImplementedError
 
+    @abstractmethod
     def set_cache(self, cache):
         """Use the specified cache to store recently decoded slide tiles.
 
@@ -176,7 +188,10 @@ def __init__(self, filename):
         """Open a whole-slide image."""
         AbstractSlide.__init__(self)
         self._filename = filename
-        self._osr = lowlevel.open(str(filename))
+        try:
+            self._osr = lowlevel.open(os.fspath(filename))
+        except TypeError:
+            raise OpenSlideUnsupportedFormatError
         if lowlevel.read_icc_profile.available:
             self._profile = lowlevel.read_icc_profile(self._osr)
 
@@ -188,7 +203,7 @@ def detect_format(cls, filename):
         """Return a string describing the format vendor of the specified file.
 
         If the file format is not recognized, return None."""
-        return lowlevel.detect_vendor(str(filename))
+        return lowlevel.detect_vendor(os.fspath(filename))
 
     def close(self):
         """Close the OpenSlide object."""
@@ -281,6 +296,7 @@ def __len__(self):
     def __iter__(self):
         return iter(self._keys())
 
+    @abstractmethod
     def _keys(self):
         # Private method; always returns list.
         raise NotImplementedError()
@@ -350,7 +366,7 @@ def __init__(self, file):
             self._image = file
         else:
             self._close = True
-            self._image = Image.open(file)
+            self._image = Image.open(os.fspath(file))
         self._profile = self._image.info.get('icc_profile')
 
     def __repr__(self):
@@ -362,15 +378,16 @@ def detect_format(cls, filename):
 
         If the file format is not recognized, return None."""
         try:
-            with Image.open(filename) as img:
+            with Image.open(os.fspath(filename)) as img:
                 return img.format
         except OSError:
             return None
 
     def close(self):
         """Close the slide object."""
         if self._close:
-            self._image.close()
+            if self._image is not None:
+                self._image.close()
             self._close = False
         self._image = None
 
@@ -379,12 +396,18 @@ def level_count(self):
         """The number of levels in the image."""
         return 1
 
+    @property
+    def _image_size(self):
+        if self._image is None:
+            raise AttributeError("Cannot read from an already closed slide")
+        return self._image.size
+
     @property
     def level_dimensions(self):
         """A list of (width, height) tuples, one for each level of the image.
 
         level_dimensions[n] contains the dimensions of level n."""
-        return (self._image.size,)
+        return (self._image_size,)
 
     @property
     def level_downsamples(self):
@@ -422,15 +445,17 @@ def read_region(self, location, level, size):
             raise OpenSlideError("Invalid level")
         if ['fail' for s in size if s < 0]:
             raise OpenSlideError(f"Size {size} must be non-negative")
+        if self._image is None:
+            raise AttributeError("Cannot read from an already closed slide")
         # Any corner of the requested region may be outside the bounds of
         # the image.  Create a transparent tile of the correct size and
         # paste the valid part of the region into the correct location.
         image_topleft = [
-            max(0, min(l, limit - 1)) for l, limit in zip(location, self._image.size)
+            max(0, min(l, limit - 1)) for l, limit in zip(location, self._image_size)
         ]
         image_bottomright = [
             max(0, min(l + s - 1, limit - 1))
-            for l, s, limit in zip(location, size, self._image.size)
+            for l, s, limit in zip(location, size, self._image_size)
         ]
         tile = Image.new("RGBA", size, (0,) * 4)
         if not [

openslide/lowlevel.py

@@ -59,34 +59,36 @@ def try_load(names):
             except OSError:
                 if name == names[-1]:
                     raise
+        raise FileNotFoundError
 
-    if platform.system() == 'Windows':
-        try:
+    library_name = "library"
+    err_hint = "Is OpenSlide installed correctly?"
+    try:
+        if platform.system() == 'Windows':
+            library_name = "DLL"
+            err_hint = "Did you call os.add_dll_directory()?"
             return try_load(['libopenslide-1.dll', 'libopenslide-0.dll'])
-        except FileNotFoundError:
-            raise ModuleNotFoundError(
-                "Couldn't locate OpenSlide DLL.  "
-                "Did you call os.add_dll_directory()?  "
-                "https://openslide.org/api/python/#installing"
-            )
-    elif platform.system() == 'Darwin':
-        try:
-            return try_load(['libopenslide.1.dylib', 'libopenslide.0.dylib'])
-        except OSError:
-            # 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).
-            import ctypes.util
-
-            lib = ctypes.util.find_library('openslide')
-            if lib is None:
-                raise ModuleNotFoundError(
-                    "Couldn't locate OpenSlide dylib.  Is OpenSlide installed "
-                    "correctly?  https://openslide.org/api/python/#installing"
-                )
-            return cdll.LoadLibrary(lib)
-    else:
-        return try_load(['libopenslide.so.1', 'libopenslide.so.0'])
+        elif platform.system() == 'Darwin':
+            library_name = "dylib"
+            try:
+                return try_load(['libopenslide.1.dylib', 'libopenslide.0.dylib'])
+            except OSError:
+                # 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).
+                import ctypes.util
+
+                lib = ctypes.util.find_library('openslide')
+                if lib is None:
+                    raise FileNotFoundError
+                return cdll.LoadLibrary(lib)
+        else:
+            return try_load(['libopenslide.so.1', 'libopenslide.so.0'])
+    except FileNotFoundError:
+        raise ModuleNotFoundError(
+            f"Couldn't locate OpenSlide {library_name}.  {err_hint}  "
+            "https://openslide.org/api/python/#installing"
+        )
 
 
 _lib = _load_library()
@@ -446,7 +448,6 @@ def read_associated_image_icc_profile(slide, name):
     'openslide_set_cache',
     None,
     [_OpenSlide, _OpenSlideCache],
-    None,
     minimum_version='4.0.0',
 )