Sample code for the callable instances article

Author: lpozo

python-callable-instances/README.md

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+# Python's .__call__() Method: Creating Callable Instances
+
+This folder provides the code examples for the Real Python tutorial [Python's .__call__() Method: Creating Callable Instances](https://realpython.com/python-callable-instances/).

python-callable-instances/counter.py

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+class Counter:
+    def __init__(self):
+        self.count = 0
+
+    def increment(self):
+        self.count += 1
+
+    def __call__(self):
+        self.increment()

python-callable-instances/cum_average.py

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+def cumulative_average():
+    sample = []
+
+    def average(new_value):
+        sample.append(new_value)
+        return sum(sample) / len(sample)
+
+    return average
+
+
+class CumulativeAverager:
+    def __init__(self):
+        self.sample = []
+
+    def __call__(self, new_value):
+        self.sample.append(new_value)
+        return sum(self.sample) / len(self.sample)

python-callable-instances/factorial.py

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+class Factorial:
+    def __init__(self):
+        self.cache = {0: 1, 1: 1}
+
+    def __call__(self, number):
+        if number in self.cache:
+            return self.cache[number]
+        else:
+            self.cache[number] = number * self.__call__(number - 1)
+            return self.cache[number]

python-callable-instances/gui.py

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+class MainWindow:
+    def show(self):
+        print("Showing the app's main window...")
+
+    def __call__(self):
+        self.show()
+
+
+window = MainWindow()
+window.show()  # Or just window()

python-callable-instances/init_vs_call.py

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+class Demo:
+    def __init__(self, attr):
+        print(f"Initialize an instance of {self.__class__.__name__}")
+        self.attr = attr
+        print(f"{self.attr=}")
+
+    def __call__(self, arg):
+        print(f"Call an instance of {self.__class__.__name__} with {arg}")

python-callable-instances/power.py

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+class PowerFactory:
+    def __init__(self, exponent):
+        self.exponent = exponent
+
+    def __call__(self, base):
+        return base**self.exponent

python-callable-instances/serializing.py

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+import json
+
+import yaml
+
+
+class JsonSerializer:
+    def __call__(self, data):
+        return json.dumps(data, indent=4)
+
+
+class YamlSerializer:
+    def __call__(self, data):
+        return yaml.dump(data)
+
+
+class DataSerializer:
+    def __init__(self, serializer_strategy):
+        self.serializer_strategy = serializer_strategy
+
+    def serialize(self, data):
+        return self.serializer_strategy(data)

python-callable-instances/shopping.py

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+from typing import NamedTuple
+
+
+class Item(NamedTuple):
+    name: str
+    price: float
+    quantity: int = 1
+
+
+class ShoppingCart:
+    def __init__(self):
+        self._cart = []
+        self._total = 0.0
+
+    def add_item(self, item):
+        self._cart.append(item)
+        self._total += item.price * item.quantity
+
+    def remove_item(self, item):
+        for cart_item in self._cart:
+            if cart_item.name == item.name:
+                self._total -= cart_item.price * cart_item.quantity
+                self._cart.remove(cart_item)
+                break
+
+    def content(self):
+        print("Items in cart:")
+        for item in self._cart:
+            print(
+                f"- {item.name}: {item.quantity} x ${item.price:.2f}"
+                f" = ${item.quantity * item.price:.2f}"
+            )
+        print(f"\nTotal: ${self._total:.2f}")
+
+    def __call__(self):
+        print("Resetting the cart...")
+        self._cart = []
+        self._total = 0.0

python-callable-instances/timing.py

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+import time
+
+# class time_execution:
+#     def __init__(self, func):
+#         self.func = func
+
+#     def __call__(self, *args, **kwargs):
+#         start = time.time()
+#         result = self.func(*args, **kwargs)
+#         end = time.time()
+#         print(f"{self.func.__name__}() takes {(end - start) * 1000:.4f} ms")
+#         return result
+
+
+class time_execution:
+    def __init__(self, repetitions=1):
+        self.repetitions = repetitions
+
+    def __call__(self, func):
+        def _timer(*args, **kwargs):
+            result = func(*args, **kwargs)
+            total_time = 0
+            print(f"Running {func.__name__}() {self.repetitions} times")
+            for _ in range(self.repetitions):
+                start = time.time()
+                func(*args, **kwargs)
+                end = time.time()
+                total_time += end - start
+            average_time = total_time / self.repetitions
+            print(
+                f"{func.__name__}() takes "
+                f"{average_time * 1000:.4f} ms on average"
+            )
+            return result
+
+        return _timer