Merge pull request #454 from realpython/python-double-underscore

Sample code for the article on underscores in Python names

python-double-underscore/README.md

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+# Single and Double Underscores in Python Names
+
+This folder provides the code examples for the Real Python tutorial [Single and Double Underscores in Python Names](https://realpython.com/python-double-underscore/).

python-double-underscore/cart.py

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+class ShoppingCart:
+    def __init__(self, customer_id):
+        self.customer_id = customer_id
+        self.products = []
+
+    def add_product(self, product):
+        self.products.append(product)
+
+    def get_products(self):
+        return self.products
+
+    def __len__(self):
+        return len(self.products)
+
+    # Implementation...

python-double-underscore/count.py

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+_count = 0
+
+
+def increment():
+    global _count
+    _count += 1
+
+
+def decrement():
+    global _count
+    _count -= 1
+
+
+def get_count():
+    return _count

python-double-underscore/csv_data.py

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+# csv_data.py
+
+import csv
+
+
+class CSVFileManager:
+    def __init__(self, file_path):
+        self.file_path = file_path
+
+    def read_csv(self):
+        return self._read(delimiter=",")
+
+    def read_tsv(self):
+        return self._read(delimiter="\t")
+
+    def _read(self, delimiter):
+        with open(self.file_path, mode="r") as file:
+            data = [row for row in csv.reader(file, delimiter=delimiter)]
+        return data

python-double-underscore/passenger.py

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+class Passenger:
+    def __init__(self, name, class_, seat):
+        self.name = name
+        self.class_ = class_
+        self.seat = seat
+
+    # Implementation...

python-double-underscore/point.py

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+class Point:
+    def __init__(self, x, y):
+        self._x = x
+        self._y = y
+
+    @property
+    def x(self):
+        return self._x
+
+    @x.setter
+    def x(self, value):
+        self._x = _validate(value)
+
+    @property
+    def y(self):
+        return self._y
+
+    @y.setter
+    def y(self, value):
+        self._y = _validate(value)
+
+
+def _validate(value):
+    if not isinstance(value, int | float):
+        raise ValueError("number expected")
+    return value

python-double-underscore/shapes.py

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+_PI = 3.14
+
+
+class Circle:
+    def __init__(self, radius):
+        self.radius = _validate(radius)
+
+    def calculate_area(self):
+        return round(_PI * self.radius**2, 2)
+
+
+class Square:
+    def __init__(self, side):
+        self.side = _validate(side)
+
+    def calculate_area(self):
+        return round(self.side**2, 2)
+
+
+def _validate(value):
+    if not isinstance(value, int | float) or value <= 0:
+        raise ValueError("positive number expected")
+    return value