class & static and cls methods

src/advance/class.py

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+class MyClass:
+    pass
+
+
+person = MyClass()
+
+
+class Car:
+    # See show_wheels method to access
+    wheels = 4  # class attribute shared by all cars (static variable)
+
+    # Constructor
+    def __init__(self,  name, origin_location, price):
+        print("Hello")
+        self.name = name
+        self.origin_location = origin_location
+        # __ makes it private
+        self.__price = price  # private attribute
+        # _original_cost is "internal use"
+        # It does not prevent access from outside the class; it’s just a hint to developers
+        self._original_cost = price
+
+    # The first parameter is always self, which refers to the instance.
+    def start_engine(self):
+        print(f"{self.name}'s Engine is starting...")
+
+    @classmethod
+    def show_wheels(cls):
+        print(f"All cars have {cls.wheels} wheels")
+
+    # The normal constructor is __init__.
+    # An alternate constructor is a class method that returns an instance of the class .
+    # Uses @ classmethod decorator.
+    # The first parameter is cls(the class itself).
+
+    @classmethod
+    def from_string(cls, string_value):
+        # Assume format: "Name-Origin_location-Price"
+        name, origin_location, price = string_value.split('-')
+        # create instance using main __init__
+        return cls(name, origin_location, price)
+
+    @classmethod
+    def from_dict(cls, data: dict):
+        # get() is dict method to get the value from dict if value is missing it gives default
+        return cls(data.get('name', ''),  data.get('origin_location', None), data.get('price', 10_000_000),)
+
+    # toString method(dart)
+    def __str__(self):
+        return f"Car( name: {self.name}, origin_location: {self.origin_location}, price: {self.__price}, wheels: {Car.wheels} )"
+
+    @staticmethod
+    def car_info():
+        print("Cars are vehicles with wheels")
+
+
+car = Car("Audi", "German", 30_000_000)
+car2 = Car("Maruthi", "India", 15_000_000)
+
+print(car.name)
+print(car.origin_location)
+print(car)
+car.start_engine()
+car2.start_engine()
+print()
+print("car wheels befor ==>", car.wheels)
+print("car wheels befor ==>", car2.wheels)
+
+Car.wheels = 5  # class attribute shared by all cars
+print()
+print("car wheels after ==>", car.wheels)
+print("car wheels after ==>", car2.wheels)
+print()
+
+# print(car.__price) # Error, cannot access directly
+print(car._original_cost)  # Works, but intended as internal
+Car.show_wheels()
+
+car3 = Car.from_string('BMW-GERMAN-13_000_000')
+
+print(car3)
+
+dict_value = {
+    "name": "Tata",
+    "price": "10_000_000",
+    "origin_location": "india",
+}
+car4 = Car.from_dict(dict_value)
+print(car4)
+
+Car.car_info()