ch25: added checkeddeco example

25-class-metaprog/checkeddeco/checkeddeco_demo.py

@@ -0,0 +1,22 @@
+from checkeddeco import checked
+
+@checked
+class Movie:
+    title: str
+    year: int
+    megabucks: float
+
+
+if __name__ == '__main__':
+    movie = Movie(title='The Godfather', year=1972, megabucks=137)
+    print(movie.title)
+    print(movie)
+    try:
+        # remove the "type: ignore" comment to see Mypy error
+        movie.year = 'MCMLXXII'  # type: ignore
+    except TypeError as e:
+        print(e)
+    try:
+        blockbuster = Movie(title='Avatar', year=2009, megabucks='billions')
+    except TypeError as e:
+        print(e)