fix function execution mutable list issue

test/test_evaluate/test_representation.py

@@ -0,0 +1,20 @@
+from jedi import Script
+
+
+def test_function_execution():
+    """
+    We've been having an issue of a mutable list that was changed inside the
+    function execution. Test if an execution always returns the same result.
+    """
+
+    s = """
+    def x():
+        return str()
+    x"""
+    d = Script(s).goto_definitions()[0]
+    # Now just use the internals of the result (easiest way to get a fully
+    # usable function).
+    func, evaluator = d._definition, d._evaluator
+    # Should return the same result both times.
+    assert len(evaluator.execute(func)) == 1
+    assert len(evaluator.execute(func)) == 1