Merge pull request realpython#479 from realpython/python-magic-methods

Sample code for the article on magic methods

Author: KateFinegan

python-magic-methods/README.md

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+# Python's Magic Methods: Leverage Their Power in Your Classes
+
+This folder provides the code examples for the Real Python tutorial [Python's Magic Methods: Leverage Their Power in Your Classes](https://realpython.com/python-magic-methods/).

python-magic-methods/bitwise_number.py

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+class BitwiseNumber:
+ def __init__(self, value):
+ self.value = value
+
+ def __and__(self, other):
+ return type(self)(self.value & other.value)
+
+ def __or__(self, other):
+ return type(self)(self.value | other.value)
+
+ def __xor__(self, other):
+ return type(self)(self.value ^ other.value)
+
+ def __invert__(self):
+ return type(self)(~self.value)
+
+ def __lshift__(self, places):
+ return type(self)(self.value << places)
+
+ def __rshift__(self, places):
+ return type(self)(self.value >> places)
+
+ def __repr__(self):
+ return bin(self.value)

python-magic-methods/circle.py

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+import math
+
+
+class Circle:
+ def __init__(self, radius):
+ self.radius = radius
+
+ def area(self):
+ return math.pi * self.radius**2
+
+ def perimeter(self):
+ return 2 * math.pi * self.radius
+
+ def __getattribute__(self, name):
+ print(f"__getattribute__ called for '{name}'")
+ return super().__getattribute__(name)
+
+ def __getattr__(self, name):
+ print(f"__getattr__ called for '{name}'")
+ if name == "diameter":
+ return self.radius * 2
+ return super().__getattr__(name)
+
+ def __setattr__(self, name, value):
+ print(f"__setattr__ called for '{name}'")
+ if name == "radius":
+ if not isinstance(value, int | float):
+ raise TypeError("radius must be a number")
+ if value <= 0:
+ raise ValueError("radius must be positive")
+ super().__setattr__(name, value)

python-magic-methods/distance.py

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+class Distance:
+ _multiples = {
+ "mm": 0.001,
+ "cm": 0.01,
+ "m": 1,
+ "km": 1_000,
+ }
+
+ def __init__(self, value, unit="m"):
+ self.value = value
+ self.unit = unit.lower()
+
+ def to_meter(self):
+ return self.value * type(self)._multiples[self.unit]
+
+ def __add__(self, other):
+ return self._compute(other, "+")
+
+ def __sub__(self, other):
+ return self._compute(other, "-")
+
+ def _compute(self, other, operator):
+ operation = eval(f"{self.to_meter()} {operator} {other.to_meter()}")
+ cls = type(self)
+ return cls(operation / cls._multiples[self.unit], self.unit)
+
+ def __radd__(self, other):
+ return self + other
+
+ def __str__(self):
+ return str(self.value) + self.unit
+
+ def __repr__(self):
+ return f"{type(self).__name__}(value={self.value}, unit={self.unit})"

python-magic-methods/factorial.py

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+class Factorial:
+ def __init__(self):
+ self._cache = {0: 1, 1: 1}
+
+ def __call__(self, number):
+ if number not in self._cache:
+ self._cache[number] = number * self(number - 1)
+ return self._cache[number]

python-magic-methods/fibonacci.py

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+class FibonacciIterator:
+ def __init__(self, stop=10):
+ self._stop = stop
+ self._index = 0
+ self._current = 0
+ self._next = 1
+
+ def __iter__(self):
+ return self
+
+ def __next__(self):
+ if self._index < self._stop:
+ self._index += 1
+ fib_number = self._current
+ self._current, self._next = (
+ self._next,
+ self._current + self._next,
+ )
+ return fib_number
+ else:
+ raise StopIteration

python-magic-methods/number.py

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+class Number:
+ def __init__(self, value):
+ self.value = value
+
+ def __add__(self, other):
+ print("__add__ called")
+ if isinstance(other, Number):
+ return Number(self.value + other.value)
+ elif isinstance(other, int | float):
+ return Number(self.value + other)
+ else:
+ raise TypeError("unsupported operand type for +")
+
+ def __radd__(self, other):
+ print("__radd__ called")
+ return self.__add__(other)
+
+ def __iadd__(self, other):
+ print("__iadd__ called")
+ return self.__add__(other)
+
+ def __str__(self):
+ return str(self.value)

python-magic-methods/person.py

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+class Person:
+ def __init__(self, name, age):
+ self.name = name
+ self.age = age
+
+ def __str__(self):
+ return f"I'm {self.name}, and I'm {self.age} years old."
+
+ def __repr__(self):
+ return f"{type(self).__name__}(name='{self.name}', age={self.age})"

python-magic-methods/point.py

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+class Point:
+ def __init__(self, x, y):
+ self.x = x
+ self.y = y
+
+ def __eq__(self, other):
+ if not isinstance(other, type(self)):
+ raise TypeError(f"'other' must be of type '{type(self).__name__}'")
+ return self.x == other.x and self.y == other.y
+
+ def __lt__(self, other):
+ if not isinstance(other, type(self)):
+ raise TypeError(f"'other' must be of type '{type(self).__name__}'")
+ return self.x < other.x and self.y < other.y
+
+ def __gt__(self, other):
+ if not isinstance(other, type(self)):
+ raise TypeError(f"'other' must be of type '{type(self).__name__}'")
+ return self.x > other.x and self.y > other.y
+
+ def __le__(self, other):
+ if not isinstance(other, type(self)):
+ raise TypeError(f"'other' must be of type '{type(self).__name__}'")
+ return self.x <= other.x and self.y <= other.y
+
+ def __ge__(self, other):
+ if not isinstance(other, type(self)):
+ raise TypeError(f"'other' must be of type '{type(self).__name__}'")
+ return self.x >= other.x and self.y >= other.y
+
+ def __ne__(self, other):
+ if not isinstance(other, type(self)):
+ raise TypeError(f"'other' must be of type '{type(self).__name__}'")
+ return self.x != other.x and self.y != other.y

python-magic-methods/reader.py

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+class TextFileReader:
+ def __init__(self, file_path):
+ self.file_path = file_path
+
+ def __enter__(self):
+ self.file_obj = open(self.file_path, mode="r")
+ return self.file_obj
+
+ def __exit__(self, exc_type, exc_val, exc_tb):
+ self.file_obj.close()