Add type hints example for duck typing

Author: gjbex

source-code/typing/README.md

@@ -23,3 +23,13 @@ Type checking can be done using [mypy](http://mypy-lang.org/index.html).
     which is a type error.
 1. `people_incorrect.py`: code that defines a `People` class, stores some
     in a list with mistakes.
+1. `duck_typing.py`: example code illustrating duck typing.
+1. `duck_typing_wrong.py`: example code illustrating duck typing, but
+   with an error.
+1. `typed_duck_typing.py`: example code illustrating duck typing
+   using type hints.
+1. `typed_duck_typing_wrong.py`: example code illustrating duck typing
+   using type hints with an error.
+1. `typed_duck_typing_false_positive.py`: example code illustrating
+   duck typing using type hints for which mypy 0.910 generates a
+   false positive.

source-code/typing/duck_typing.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python
+import argparse
+
+class Duck:
+
+    def make_sound(self):
+        print('quack')
+
+
+class AlarmClock:
+
+    def make_sound(self):
+        print('ring-ring')
+
+
+def sound_repeater(sound_maker, nr_repeats):
+    for _ in range(nr_repeats):
+        sound_maker.make_sound()
+
+
+if __name__ == '__main__':
+    arg_parser = argparse.ArgumentParser(description='sound maker')
+    arg_parser.add_argument('--type', choices=['duck', 'alarm'],
+                            help='sound source')
+    arg_parser.add_argument('--n', type=int, default=1,
+                            help='number of sounds to make')
+    options = arg_parser.parse_args()
+    sound_maker = Duck() if options.type == 'duck' else AlarmClock()
+    sound_repeater(sound_maker, options.n)

source-code/typing/duck_typing_wrong.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python
+import argparse
+
+class Duck:
+
+    def quack(self):
+        print('quack')
+
+
+class AlarmClock:
+
+    def make_sound(self):
+        print('ring-ring')
+
+
+def sound_repeater(sound_maker, nr_repeats):
+    for _ in range(nr_repeats):
+        sound_maker.make_sound()
+
+
+if __name__ == '__main__':
+    arg_parser = argparse.ArgumentParser(description='sound maker')
+    arg_parser.add_argument('--type', choices=['duck', 'alarm'],
+                            help='sound source')
+    arg_parser.add_argument('--n', type=int, default=1,
+                            help='number of sounds to make')
+    options = arg_parser.parse_args()
+    sound_maker = Duck() if options.type == 'duck' else AlarmClock()
+    sound_repeater(sound_maker, options.n)

source-code/typing/typed_duck_typing.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python
+import argparse
+from typing import Protocol
+
+class SoundMaker(Protocol):
+
+    def make_sound(self) -> None:
+        pass
+
+
+class Duck:
+
+    def make_sound(self) -> None:
+        print('quack')
+
+
+class AlarmClock:
+
+    def make_sound(self) -> None:
+        print('ring-ring')
+
+
+def sound_repeater(sound_maker: SoundMaker, nr_repeats: int):
+    for _ in range(nr_repeats):
+        sound_maker.make_sound()
+
+
+if __name__ == '__main__':
+    arg_parser = argparse.ArgumentParser(description='sound maker')
+    arg_parser.add_argument('--type', choices=['duck', 'alarm'],
+                            help='sound source')
+    arg_parser.add_argument('--n', type=int, default=1,
+                            help='number of sounds to make')
+    options = arg_parser.parse_args()
+    sound_maker: SoundMaker
+    if options.type == 'duck':
+        sound_maker = Duck()
+    else:
+        sound_maker = AlarmClock()
+    sound_repeater(sound_maker, options.n)

source-code/typing/typed_duck_typing_false_positive.py

@@ -0,0 +1,36 @@
+#!/usr/bin/env python
+import argparse
+from typing import Protocol
+
+class SoundMaker(Protocol):
+
+    def make_sound(self) -> None:
+        pass
+
+
+class Duck:
+
+    def make_sound(self) -> None:
+        print('quack')
+
+
+class AlarmClock:
+
+    def make_sound(self) -> None:
+        print('ring-ring')
+
+
+def sound_repeater(sound_maker: SoundMaker, nr_repeats: int):
+    for _ in range(nr_repeats):
+        sound_maker.make_sound()
+
+
+if __name__ == '__main__':
+    arg_parser = argparse.ArgumentParser(description='sound maker')
+    arg_parser.add_argument('--type', choices=['duck', 'alarm'],
+                            help='sound source')
+    arg_parser.add_argument('--n', type=int, default=1,
+                            help='number of sounds to make')
+    options = arg_parser.parse_args()
+    sound_maker: SoundMaker = Duck() if options.type == 'duck' else AlarmClock()
+    sound_repeater(sound_maker, options.n)

source-code/typing/typed_duck_typing_wrong.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python
+import argparse
+from typing import Protocol
+
+class SoundMaker(Protocol):
+
+    def make_sound(self) -> None:
+        pass
+
+
+class Duck:
+
+    def quack(self) -> None:
+        print('quack')
+
+
+class AlarmClock:
+
+    def make_sound(self) -> None:
+        print('ring-ring')
+
+
+def sound_repeater(sound_maker: SoundMaker, nr_repeats: int):
+    for _ in range(nr_repeats):
+        sound_maker.make_sound()
+
+
+if __name__ == '__main__':
+    arg_parser = argparse.ArgumentParser(description='sound maker')
+    arg_parser.add_argument('--type', choices=['duck', 'alarm'],
+                            help='sound source')
+    arg_parser.add_argument('--n', type=int, default=1,
+                            help='number of sounds to make')
+    options = arg_parser.parse_args()
+    sound_maker: SoundMaker
+    if options.type == 'duck':
+        sound_maker = Duck()
+    else:
+        sound_maker = AlarmClock()
+    sound_repeater(sound_maker, options.n)