الطرق السحرية: __str__ و__repr__

ما الطرق السحرية؟

class Foo:
    def __str__(self):
        return "I am Foo"

f = Foo()
print(f)        # I am Foo
print(str(f))   # I am Foo

__repr__: تمثيل المطوّر

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __repr__(self):
        return f"Point({self.x}, {self.y})"

p = Point(3, 4)
print(repr(p))  # Point(3, 4)

__str__: تمثيل المستخدم

class Temperature:
    def __init__(self, celsius):
        self.celsius = celsius

    def __str__(self):
        return f"{self.celsius}°C"

    def __repr__(self):
        return f"Temperature({self.celsius})"

t = Temperature(100)
print(t)        # 100°C
print(repr(t))  # Temperature(100)

متى تُستدعى كل طريقة؟

class Item:
    def __str__(self): return "str"
    def __repr__(self): return "repr"

x = Item()
print(x)         # str
print([x])       # [repr]  ← list uses repr for elements

__format__ للتنسيق المخصص

class Money:
    def __init__(self, amount):
        self.amount = amount

    def __format__(self, spec):
        if spec == "usd":
            return f"${self.amount:.2f}"
        return str(self.amount)

m = Money(9.5)
print(f"{m:usd}")  # $9.50

__bool__ للقيمة المنطقية

class Bag:
    def __init__(self, items):
        self.items = items

    def __bool__(self):
        return len(self.items) > 0

b = Bag([])
if not b:
    print("Bag is empty")  # Bag is empty

__len__ للدالة len()

class Stack:
    def __init__(self):
        self.data = []

    def push(self, v): self.data.append(v)

    def __len__(self):
        return len(self.data)

s = Stack()
s.push(1)
print(len(s))  # 1

__eq__ للمساواة

class Vector:
    def __init__(self, x, y):
        self.x, self.y = x, y

    def __eq__(self, other):
        return self.x == other.x and self.y == other.y

print(Vector(1,2) == Vector(1,2))  # True

__hash__ مع __eq__

class Point:
    def __init__(self, x, y): self.x, self.y = x, y
    def __eq__(self, o): return (self.x, self.y) == (o.x, o.y)
    def __hash__(self): return hash((self.x, self.y))

pts = {Point(1,2), Point(1,2)}
print(len(pts))  # 1

__add__ والعمليات الحسابية

class Vector:
    def __init__(self, x, y): self.x, self.y = x, y
    def __add__(self, o): return Vector(self.x+o.x, self.y+o.y)
    def __repr__(self): return f"Vector({self.x},{self.y})"

print(Vector(1,2) + Vector(3,4))  # Vector(4,6)

__getitem__ للفهرسة

class Matrix:
    def __init__(self, data):
        self.data = data

    def __getitem__(self, idx):
        return self.data[idx]

m = Matrix([[1,2],[3,4]])
print(m[0])     # [1, 2]
print(m[1][0])  # 3

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