Disallow multiple base classes (fix #14)

mypy/semanal.py

@@ -299,10 +299,23 @@ class SemanticAnalyzer(NodeVisitor):
             for t in bt[1:]:
                 if isinstance(t, Instance):
                     defn.info.add_interface(((Instance)t).type)
+        self.verify_base_classes(defn)
         defn.defs.accept(self)
         self.locals.pop()
         self.type, self.class_tvars = self.type_stack.pop()
-
+
+    void verify_base_classes(self, TypeDef defn):
+        base_classes = <str> []
+        for base in defn.base_types:
+            if isinstance(base, Instance):
+                baseinfo = ((Instance)base).type
+                if not baseinfo.is_interface:
+                    base_classes.append(baseinfo.name())
+        if len(base_classes) > 1:
+            bases = ["'%s'" % n for n in sorted(base_classes)]
+            self.fail('Class has multiple base classes (%s)' %
+                      (' and '.join(bases)), defn)
+
     Type object_type(self):
         sym = self.lookup_qualified('__builtins__.object', None)
         return Instance((TypeInfo)sym.node, [])

test/data/pythongen.test

@@ -67,10 +67,10 @@ class A<t>:
 class A:
     pass
 
-[case testGenericBaseClass]
+[case testGenericBaseType]
 class A(B<object>, C<any, object>):
     pass
-class B<t>: pass
+interface B<t>: pass
 class C<t, s>: pass
 [out]
 class A(B, C):

test/data/semanal-errors.test

@@ -503,3 +503,9 @@ class A<t>:
         A<t> x # E: Name 't' is not defined
     A<s> y # E: Name 's' is not defined
 [out]
+
+[case testExtendMultipleClasses]
+class A: pass
+class B: pass
+class C(A, B): pass # E: Class has multiple base classes ('A' and 'B')
+[out]