bpo-19610: setup() now raises TypeError for invalid types (GH-4519)

The Distribution class now explicitly raises an
exception when 'classifiers', 'keywords' and
'platforms' fields are not specified as a list.

Lib/distutils/dist.py

@@ -1188,12 +1188,38 @@ class DistributionMetadata:
     def get_keywords(self):
         return self.keywords or []
 
+    def set_keywords(self, value):
+        # If 'keywords' is a string, it will be converted to a list
+        # by Distribution.finalize_options(). To maintain backwards
+        # compatibility, do not raise an exception if 'keywords' is
+        # a string.
+        if not isinstance(value, (list, str)):
+            msg = "'keywords' should be a 'list', not %r"
+            raise TypeError(msg % type(value).__name__)
+        self.keywords = value
+
     def get_platforms(self):
         return self.platforms or ["UNKNOWN"]
 
+    def set_platforms(self, value):
+        # If 'platforms' is a string, it will be converted to a list
+        # by Distribution.finalize_options(). To maintain backwards
+        # compatibility, do not raise an exception if 'platforms' is
+        # a string.
+        if not isinstance(value, (list, str)):
+            msg = "'platforms' should be a 'list', not %r"
+            raise TypeError(msg % type(value).__name__)
+        self.platforms = value
+
     def get_classifiers(self):
         return self.classifiers or []
 
+    def set_classifiers(self, value):
+        if not isinstance(value, list):
+            msg = "'classifiers' should be a 'list', not %r"
+            raise TypeError(msg % type(value).__name__)
+        self.classifiers = value
+
     def get_download_url(self):
         return self.download_url or "UNKNOWN"