TIL: Defining method outside of class

python/defining-method-outside-of-class.md

@@ -0,0 +1,20 @@
+You can define methods outside of class definition. However, you need to make sure that you bound the method *to the class* itself **not** instance.
+
+```python
+class Foo:
+    x = 42
+
+
+def bar(self):
+    return self.x
+
+
+if __name__ == "__main__":
+    foo = Foo()
+
+    Foo.bar = bar
+    print(foo.bar())  # 42
+
+    foo.bar = bar
+    print(foo.bar())  # error, because `bar` doesn't know about `self`
+```