Replace can_open() method with detect_format()

OpenSlide calls it detect_vendor(), but "format" makes more sense for
ImageSlide.

Author: bgilbert

README.txt

@@ -1,7 +1,7 @@
 OpenSlide Python requires:
 
 * Python 2 >= 2.6 or Python 3 >= 3.3
-* OpenSlide >= 3.3.0
+* OpenSlide >= 3.4.0
 * Python Imaging Library or Pillow
 
 To install:

openslide/__init__.py

@@ -56,8 +56,10 @@ def __exit__(self, exc_type, exc_val, exc_tb):
         return False
 
     @classmethod
-    def can_open(cls, filename):
-        """Return True if the specified file can be read."""
+    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
 
     def close(self):
@@ -150,9 +152,11 @@ def __init__(self, filename):
         self._osr = lowlevel.open(filename)
 
     @classmethod
-    def can_open(cls, filename):
-        """Return True if OpenSlide can read the specified file."""
-        return lowlevel.can_open(filename)
+    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(filename)
 
     def close(self):
         """Close the OpenSlide object."""
@@ -267,13 +271,14 @@ def __init__(self, file):
             self._image = Image.open(file)
 
     @classmethod
-    def can_open(cls, filename):
-        """Return True if PIL can read the specified file."""
+    def detect_format(cls, filename):
+        """Return a string describing the format of the specified file.
+
+        If the file format is not recognized, return None."""
         try:
-            Image.open(filename)
-            return True
+            return Image.open(filename).format
         except IOError:
-            return False
+            return None
 
     def close(self):
         """Close the slide object."""
@@ -360,8 +365,8 @@ def open_slide(filename):
 
 if __name__ == '__main__':
     import sys
-    print("OpenSlide can open:", OpenSlide.can_open(sys.argv[1]))
-    print("PIL can open:", ImageSlide.can_open(sys.argv[1]))
+    print("OpenSlide vendor:", OpenSlide.detect_format(sys.argv[1]))
+    print("PIL format:", ImageSlide.detect_format(sys.argv[1]))
     with open_slide(sys.argv[1]) as _slide:
         print("Dimensions:", _slide.dimensions)
         print("Levels:", _slide.level_count)

openslide/lowlevel.py

@@ -171,11 +171,10 @@ def _load_image(buf, size):
     return PIL.Image.frombuffer('RGBA', size, buf, 'raw', 'RGBa', 0, 1)
 
 try:
-    get_version = _func('openslide_get_version', c_char_p, [], _check_string)
+    detect_vendor = _func('openslide_detect_vendor', c_char_p, [_utf8_p],
+            _check_string)
 except AttributeError:
-    raise OpenSlideError('OpenSlide >= 3.3.0 required')
-
-can_open = _func('openslide_can_open', c_bool, [_utf8_p], None)
+    raise OpenSlideError('OpenSlide >= 3.4.0 required')
 
 open = _func('openslide_open', c_void_p, [_utf8_p], _check_open)
 
@@ -240,3 +239,5 @@ def read_associated_image(slide, name):
     buf = (w * h * c_uint32)()
     _read_associated_image(slide, name, buf)
     return _load_image(buf, (w, h))
+
+get_version = _func('openslide_get_version', c_char_p, [], _check_string)