Python: Extend DuckTyping module

Adds `overridesMethod` and `isPropertyAccessor`.

Author: tausbn

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll

@@ -2111,4 +2111,27 @@ module DuckTyping {
       )
     )
   }
+
+  /**
+   * Gets the `__init__` function that will be invoked when `cls` is constructed,
+   * resolved according to the MRO.
+   */
+  Function getInit(Class cls) { result = invokedFunctionFromClassConstruction(cls, "__init__") }
+
+  /**
+   * Holds if `f` overrides a method in a superclass with the same name.
+   */
+  predicate overridesMethod(Function f) {
+    exists(Class cls | f.getScope() = cls | hasMethod(getADirectSuperclass(cls), f.getName()))
+  }
+
+  /**
+   * Holds if `f` is a property accessor (decorated with `@property`, `@name.setter`,
+   * or `@name.deleter`).
+   */
+  predicate isPropertyAccessor(Function f) {
+    exists(Attribute a | a = f.getADecorator() | a.getName() = "setter" or a.getName() = "deleter")
+    or
+    f.getADecorator().(Name).getId() = "property"
+  }
 }