Merge pull request #497 from realpython/duck-typing-python

Sample code for the Duck typing article

duck-typing-python/README.md

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+# Duck Typing in Python: Writing Flexible and Decoupled Code
+
+This folder provides the code examples for the Real Python tutorial [Duck Typing in Python: Writing Flexible and Decoupled Code](https://realpython.com/duck-typing-python/).

duck-typing-python/birds_v1.py

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+class Duck:
+    def swim(self):
+        print("The duck is swimming")
+
+    def fly(self):
+        print("The duck is flying")
+
+
+class Swan:
+    def swim(self):
+        print("The swan is swimming")
+
+    def fly(self):
+        print("The swan is flying")
+
+
+class Albatross:
+    def swim(self):
+        print("The albatross is swimming")
+
+    def fly(self):
+        print("The albatross is flying")

duck-typing-python/birds_v2.py

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+class Duck:
+    def fly(self):
+        print("The duck is flying")
+
+    def swim(self):
+        print("The duck is swimming")
+
+
+class Pigeon:
+    def fly(self):
+        print("The pigeon is flying")

duck-typing-python/file.csv

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+name,age,job
+John,25,Engineer
+Jane,22,Designer

duck-typing-python/file.json

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+[
+    {
+        "name": "John",
+        "age": 25,
+        "job": "Engineer"
+    },
+    {
+        "name": "Jane",
+        "age": 22,
+        "job": "Designer"
+    }
+]

duck-typing-python/file.txt

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+John
+25
+Engineer
+Jane
+22
+Designer

duck-typing-python/iteration.py

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+numbers = [1, 2, 3]
+person = ("Jane", 25, "Python Dev")
+letters = "abc"
+ordinals = {"one": "first", "two": "second", "three": "third"}
+even_digits = {2, 4, 6, 8}
+collections = [numbers, person, letters, ordinals, even_digits]
+
+for collection in collections:
+    for value in collection:
+        print(value)

duck-typing-python/mean.py

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+from collections.abc import Collection
+
+
+def mean(grades: Collection) -> float:
+    return sum(grades) / len(grades)

duck-typing-python/queues.py

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+from collections import deque
+
+
+class Queue:
+    def __init__(self):
+        self._elements = deque()
+
+    def enqueue(self, element):
+        self._elements.append(element)
+
+    def dequeue(self):
+        return self._elements.popleft()
+
+    def __iter__(self):
+        return iter(self._elements)
+
+    def __len__(self):
+        return len(self._elements)
+
+    def __reversed__(self):
+        return reversed(self._elements)
+
+    def __contains__(self, element):
+        return element in self._elements

duck-typing-python/readers.py

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+import csv
+import json
+from itertools import batched  # Python >= 3.12
+
+
+class TextReader:
+    def __init__(self, filename):
+        self.filename = filename
+
+    def read(self):
+        with open(self.filename, encoding="utf-8") as file:
+            return [
+                {
+                    "name": batch[0].strip(),
+                    "age": batch[1].strip(),
+                    "job": batch[2].strip(),
+                }
+                for batch in batched(file.readlines(), 3)
+            ]
+
+
+class CSVReader:
+    def __init__(self, filename):
+        self.filename = filename
+
+    def read(self):
+        with open(self.filename, encoding="utf-8", newline="") as file:
+            return list(csv.DictReader(file))
+
+
+class JSONReader:
+    def __init__(self, filename):
+        self.filename = filename
+
+    def read(self):
+        with open(self.filename, encoding="utf-8") as file:
+            return json.load(file)

duck-typing-python/shapes.py

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+from math import pi
+from typing import Protocol
+
+
+class Shape(Protocol):
+    def area(self) -> float:
+        ...
+
+    def perimeter(self) -> float:
+        ...
+
+
+class Circle:
+    def __init__(self, radius: float) -> None:
+        self.radius = radius
+
+    def area(self) -> float:
+        return pi * self.radius**2
+
+    def perimeter(self) -> float:
+        return 2 * pi * self.radius
+
+
+class Square:
+    def __init__(self, side: float) -> None:
+        self.side = side
+
+    def area(self) -> float:
+        return self.side**2
+
+    def perimeter(self) -> float:
+        return 4 * self.side
+
+
+class Rectangle:
+    def __init__(self, length: float, width: float) -> None:
+        self.length = length
+        self.width = width
+
+    def area(self) -> float:
+        return self.length * self.width
+
+    def perimeter(self) -> float:
+        return 2 * (self.length + self.width)
+
+
+def describe_shape(shape: Shape) -> None:
+    print(f"{type(shape).__name__}")
+    print(f" Area: {shape.area():.2f}")
+    print(f" Perimeter: {shape.perimeter():.2f}")
+
+
+circle = Circle(3)
+square = Square(5)
+rectangle = Rectangle(4, 5)
+
+describe_shape(circle)
+describe_shape(square)
+describe_shape(rectangle)

duck-typing-python/vehicles_abc.py

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+from abc import ABC, abstractmethod
+
+
+class Vehicle(ABC):
+    def __init__(self, make, model, color):
+        self.make = make
+        self.model = model
+        self.color = color
+
+    @abstractmethod
+    def start(self):
+        raise NotImplementedError("This method must be implemented")
+
+    @abstractmethod
+    def stop(self):
+        raise NotImplementedError("This method must be implemented")
+
+    @abstractmethod
+    def drive(self):
+        raise NotImplementedError("This method must be implemented")
+
+
+class Car(Vehicle):
+    def start(self):
+        print("The car is starting")
+
+    def stop(self):
+        print("The car is stopping")
+
+    def drive(self):
+        print("The car is driving")
+
+
+class Truck(Vehicle):
+    def start(self):
+        print("The truck is starting")
+
+    def stop(self):
+        print("The truck is stopping")
+
+    def drive(self):
+        print("The truck is driving")

duck-typing-python/vehicles_duck.py

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+class Car:
+    def __init__(self, make, model, color):
+        self.make = make
+        self.model = model
+        self.color = color
+
+    def start(self):
+        print("The car is starting")
+
+    def stop(self):
+        print("The car is stopping")
+
+    def drive(self):
+        print("The car is driving")
+
+
+class Truck:
+    def __init__(self, make, model, color):
+        self.make = make
+        self.model = model
+        self.color = color
+
+    def start(self):
+        print("The truck is starting")
+
+    def stop(self):
+        print("The truck is stopping")
+
+    def drive(self):
+        print("The truck is driving")