Sample code for the article on closures

python-closure/README.md

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+# Python Closures: Common Use Cases and Examples
+
+This folder provides the code examples for the Real Python tutorial [Python Closures: Common Use Cases and Examples](https://realpython.com/python-closure/).

python-closure/app.py

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+import tkinter as tk
+
+app = tk.Tk()
+app.title("GUI App")
+app.geometry("320x240")
+
+label = tk.Label(app, font=("Helvetica", 16, "bold"))
+label.pack()
+
+
+def callback(text):
+    def closure():
+        label.config(text=text)
+
+    return closure
+
+
+button = tk.Button(
+    app,
+    text="Greet",
+    command=callback("Hello, World!"),
+)
+button.pack()
+
+app.mainloop()

python-closure/appender.py

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+def make_appender():
+    items = []
+
+    def appender(new_item):
+        items.append(new_item)
+        return items
+
+    return appender

python-closure/closure.py

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+# def outer_func():
+#     name = "Pythonista"
+
+#     def inner_func():
+#         print(f"Hello, {name}!")
+
+#     return inner_func
+
+
+def outer_func():
+    name = "Pythonista"
+    return lambda name=name: print(f"Hello, {name}!")
+
+
+inner_func = outer_func()
+inner_func()

python-closure/counter.py

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+def make_counter():
+    count = 0
+
+    def counter():
+        nonlocal count
+        count += 1
+        return count
+
+    return counter

python-closure/cum_average.py

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+def cumulative_average():
+    data = []
+
+    def average(value):
+        data.append(value)
+        return sum(data) / len(data)
+
+    return average

python-closure/decorators.py

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+def decorator(function):
+    def closure():
+        print("Doing something before calling the function.")
+        function()
+        print("Doing something after calling the function.")
+
+    return closure
+
+
+@decorator
+def greet():
+    print("Hi, Pythonista!")

python-closure/free_variables.py

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+def outer_func(outer_arg):
+    local_var = "Outer local variable"
+
+    def closure():
+        print(outer_arg)
+        print(local_var)
+        print(another_local_var)
+
+    another_local_var = "Another outer local variable"
+
+    return closure

python-closure/inner.py

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+def outer_func():
+    name = "Pythonista"
+
+    def inner_func():
+        print(f"Hello, {name}!")
+
+    inner_func()

python-closure/memoization.py

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+from time import sleep
+from timeit import timeit
+
+
+def memoize(function):
+    cache = {}
+
+    def closure(number):
+        if number not in cache:
+            cache[number] = function(number)
+        return cache[number]
+
+    return closure
+
+
+@memoize
+def slow_operation(number):
+    sleep(0.5)
+
+
+exec_time = timeit(
+    "[slow_operation(number) for number in [2, 3, 4, 2, 3, 4]]",
+    globals=globals(),
+    number=1,
+)
+
+print(f"Slow operation's time:   {exec_time:.2f} seconds.")

python-closure/roots.py

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+def make_root_calculator(root_degree, precision=2):
+    def root_calculator(number):
+        return round(pow(number, 1 / root_degree), precision)
+
+    return root_calculator
+
+
+square_root = make_root_calculator(2, 4)
+print(square_root(42))
+
+cubic_root = make_root_calculator(3, 2)
+print(cubic_root(42))
+
+
+class RootCalculator:
+    def __init__(self, root_degree, precision=2):
+        self.root_degree = root_degree
+        self.precision = precision
+
+    def __call__(self, number):
+        return round(pow(number, 1 / self.root_degree), self.precision)
+
+
+square_root = RootCalculator(2, 4)
+print(square_root(42))
+
+cubic_root = RootCalculator(3, 2)
+print(cubic_root(42))

python-closure/stack_v1.py

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+class Stack:
+    def __init__(self):
+        self._items = []
+
+    def push(self, item):
+        self._items.append(item)
+
+    def pop(self):
+        return self._items.pop()
+
+    def __str__(self):
+        return str(self._items)

python-closure/stack_v2.py

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+def Stack():
+    _items = []
+
+    def push(item):
+        _items.append(item)
+
+    def pop():
+        return _items.pop()
+
+    def closure():
+        pass
+
+    closure.push = push
+    closure.pop = pop
+    return closure