Separated out feature checking from selftest

PIL/features.py

@@ -0,0 +1,71 @@
+from PIL import Image
+
+modules = {
+    "PIL CORE": "PIL._imaging",
+    "TKINTER": "PIL._imagingtk",
+    "FREETYPE2": "PIL._imagingft",
+    "LITTLECMS2": "PIL._imagingcms",
+    "WEBP": "PIL._webp",
+    "Transparent WEBP": ("WEBP", "WebPDecoderBuggyAlpha")
+}
+
+
+def check_module(feature):
+    module = modules[feature]
+
+    method_to_call = None
+    if type(module) is tuple:
+        module, method_to_call = module
+
+    try:
+        imported_module = __import__(module)
+    except ImportError:
+        # If a method is being checked, None means that
+        # rather than the method failing, the module required for the method
+        # failed to be imported first
+        return None if method_to_call else False
+
+    if method_to_call:
+        method = getattr(imported_module, method_to_call)
+        return method() is True
+    else:
+        return True
+
+
+def get_supported_modules():
+    supported_modules = []
+    for feature in get_all_modules():
+        if check_module(feature):
+            supported_modules.append(feature)
+    return supported_modules
+
+
+def get_all_modules():
+    # While the dictionary keys could be used here,
+    # a static list is used to maintain order
+    return ["PIL CORE", "TKINTER", "FREETYPE2",
+            "LITTLECMS2", "WEBP", "Transparent WEBP"]
+
+codecs = {
+    "JPEG": "jpeg",
+    "JPEG 2000": "jpeg2k",
+    "ZLIB (PNG/ZIP)": "zip",
+    "LIBTIFF": "libtiff"
+}
+
+
+def check_codec(feature):
+    codec = codecs[feature]
+    return codec + "_encoder" in dir(Image.core)
+
+
+def get_supported_codecs():
+    supported_codecs = []
+    for feature in get_all_codecs():
+        if check_codec(feature):
+            supported_codecs.append(feature)
+    return supported_codecs
+
+
+def get_all_codecs():
+    return ["JPEG", "JPEG 2000", "ZLIB (PNG/ZIP)", "LIBTIFF"]

selftest.py

@@ -9,6 +9,7 @@ if "--installed" in sys.argv:
     del sys.path[0]
 
 from PIL import Image, ImageDraw, ImageFilter, ImageMath
+from PIL import features
 
 if "--installed" in sys.argv:
     sys.path.insert(0, sys_path_0)
@@ -162,22 +163,6 @@ def testimage():
     """
 
 
-def check_module(feature, module):
-    try:
-        __import__(module)
-    except ImportError:
-        print("***", feature, "support not installed")
-    else:
-        print("---", feature, "support ok")
-
-
-def check_codec(feature, codec):
-    if codec + "_encoder" not in dir(Image.core):
-        print("***", feature, "support not installed")
-    else:
-        print("---", feature, "support ok")
-
-
 if __name__ == "__main__":
     # check build sanity
 
@@ -189,23 +174,22 @@ if __name__ == "__main__":
     print("Python modules loaded from", os.path.dirname(Image.__file__))
     print("Binary modules loaded from", os.path.dirname(Image.core.__file__))
     print("-"*68)
-    check_module("PIL CORE", "PIL._imaging")
-    check_module("TKINTER", "PIL._imagingtk")
-    check_codec("JPEG", "jpeg")
-    check_codec("JPEG 2000", "jpeg2k")
-    check_codec("ZLIB (PNG/ZIP)", "zip")
-    check_codec("LIBTIFF", "libtiff")
-    check_module("FREETYPE2", "PIL._imagingft")
-    check_module("LITTLECMS2", "PIL._imagingcms")
-    check_module("WEBP", "PIL._webp")
-    try:
-        from PIL import _webp
-        if _webp.WebPDecoderBuggyAlpha():
-            print("***", "Transparent WEBP", "support not installed")
-        else:
-            print("---", "Transparent WEBP", "support ok")
-    except Exception:
+    for feature in features.get_all_modules():
+        supported = features.check_module(feature)
+
+        if supported is None:
+            # A method was being tested, but the module required
+            # for the method could not be correctly imported
             pass
+        elif supported:
+            print("---", feature, "support ok")
+        else:
+            print("***", feature, "support not installed")
+    for feature in features.get_all_codecs():
+        if features.check_codec(feature):
+            print("---", feature, "support ok")
+        else:
+            print("***", feature, "support not installed")
     print("-"*68)
 
     # use doctest to make sure the test program behaves as documented!