Add example of user-defined class type hint

Author: gjbex

source-code/typing/README.md

@@ -36,3 +36,5 @@ Type checking can be done using [mypy](http://mypy-lang.org/index.html).
    false positive.
 1. `numpy_typing.py`: illustration of a script using both numpy and
    matplotlib with type hints.
+1. `classes.py`: illustration of using type hints with a user-defined
+   class.

source-code/typing/classes.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python
+
+from typing import Any
+
+
+class MyClass:
+
+    def __init__(self, data: Any) -> None:
+        self.data = data
+
+    @property
+    def data(self) -> int:
+        return self.data
+
+    @data.setter
+    def data(self, value: Any) -> None:
+        self.data = int(value)
+
+    def __repr__(self) -> str:
+        return f'data: {self.data}'
+
+
+def print_data(data: MyClass) -> None:
+    print(data)
+
+
+if __name__ == '__main__':
+    data = MyClass('25')
+    print_data(data)