Add OpenSlideVersionError

Raise a subclass of OpenSlideError when an unsupported OpenSlide version
is detected.

Author: bgilbert

doc/index.rst

@@ -220,6 +220,11 @@ Exceptions
    OpenSlide does not support the requested file.  Subclass of
    :exc:`OpenSlideError`.
 
+.. exception:: OpenSlideVersionError
+
+   This version of OpenSlide does not support the requested functionality.
+   Subclass of :exc:`OpenSlideError`.
+
 
 Wrapping a PIL Image
 ====================

openslide/__init__.py

@@ -30,7 +30,11 @@
 
 # For the benefit of library users
 from openslide._version import __version__  # noqa: F401  module-imported-but-unused
-from openslide.lowlevel import OpenSlideError, OpenSlideUnsupportedFormatError
+from openslide.lowlevel import (  # noqa: F401  module-imported-but-unused
+    OpenSlideError,
+    OpenSlideUnsupportedFormatError,
+    OpenSlideVersionError,
+)
 
 __library_version__ = lowlevel.get_version()
 

openslide/lowlevel.py

@@ -76,6 +76,17 @@ class OpenSlideError(Exception):
     """
 
 
+class OpenSlideVersionError(OpenSlideError):
+    """This version of OpenSlide does not support the requested functionality.
+
+    Import this from openslide rather than from openslide.lowlevel.
+    """
+
+    def __init__(self, minimum_version):
+        super().__init__(f'OpenSlide >= {minimum_version} required')
+        self.minimum_version = minimum_version
+
+
 class OpenSlideUnsupportedFormatError(OpenSlideError):
     """OpenSlide does not support the requested file.
 
@@ -187,7 +198,7 @@ def _func(name, restype, argtypes, errcheck=_check_error):
 try:
     detect_vendor = _func('openslide_detect_vendor', c_char_p, [_utf8_p], _check_string)
 except AttributeError:
-    raise OpenSlideError('OpenSlide >= 3.4.0 required')
+    raise OpenSlideVersionError('3.4.0')
 
 open = _func('openslide_open', c_void_p, [_utf8_p], _check_open)