F*** bug

bug.py

@@ -0,0 +1,15 @@
+class A:
+    def __init__(self, arg=None):
+        if arg is None:
+            self.arg = {}
+
+    def set(self):
+        self.arg['something'] = 'something'
+
+
+a1 = A()
+a1.set()
+a2 = A()
+
+print(a2.arg)
+# output is {'something': 'something'}