tests/class_inplace_op: Test for inplace op fallback to normal one.

tests/basics/class_inplace_op.py

@@ -0,0 +1,47 @@
+# Case 1: Immutable object (e.g. number-like)
+# __iadd__ should not be defined, will be emulated using __add__
+
+class A:
+
+    def __init__(self, v):
+        self.v = v
+
+    def __add__(self, o):
+        return A(self.v + o.v)
+
+    def __repr__(self):
+        return "A(%s)" % self.v
+
+a = A(5)
+b = a
+a += A(3)
+print(a)
+# Should be original a's value, i.e. A(5)
+print(b)
+
+# Case 2: Mutable object (e.g. list-like)
+# __iadd__ should be defined
+
+class L:
+
+    def __init__(self, v):
+        self.v = v
+
+    def __add__(self, o):
+        # Should not be caled in this test
+        print("L.__add__")
+        return L(self.v + o.v)
+
+    def __iadd__(self, o):
+        self.v += o.v
+        return self
+
+    def __repr__(self):
+        return "L(%s)" % self.v
+
+c = L([1, 2])
+d = c
+c += L([3, 4])
+print(c)
+# Should be updated c's value, i.e. L([1, 2, 3, 4])
+print(d)