built-in functions

https://www.pythontutorial.net/python-oop/python-__repr__/

1. `str` and `repr`

	`__str__`	`__repr__`
含义	returns a string representation of an object that is human-readable, 通常如果未自定义实现,会调用`__repr__` `str()`最后调用此方法，通常`print(a)`会调用`str()`,最后调用到a的`__str__`	returns a string representation of an object that is machine-readable Typically, the `__repr__()` returns a string that can be executed and yield the same value as the object. In other words, if you pass the returned string of the `object_name.__repr__()` method to the `eval()` function, you’ll get the same value as the `object_name`


class Person:
    def __init__(self, first_name, last_name, age):
        self.first_name = first_name
        self.last_name = last_name
        self.age = age

    def __repr__(self):
        return f'Person("{self.first_name}","{self.last_name}",{self.age})'

person = Person("John", "Doe", 25)
print(repr(person))
# using str()
print(person)

2. `call`

The __call__ method allows an instance of a class to be called as if it were a function. This can be useful for objects that represent operations or transformations.


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

    def __call__(self, value):
        return value + self.amount

add_five = Adder(5)
print(add_five(10))  # Output: 15