Python：如何在同一类中创建类的实例？

Question

I am trying to create a class which has a static method which returns list of its own instances. How can I do this without referring to the class name:

 1: class MyCar(object):
 2:  def __init__(self, number):
 3:    self._num = number
 4: 
 5:  @staticmethod
 6:  def get_cars_from(start=0, end=10):
 7:    """ This method get a list of cars from number 1 to 10.
 8:    """
 9:    return_list = []
10:    for i in range(start, end):
11:      instance = MyCar(i)
12:      return_list.append(instance)
13:    return return_list

This code works perfectly fine. But I have to reuse this code (copy+paste) in various classes, like Bus, Ship, Plane, Truck .

I am looking for a way to reuse above code in all these classes by making a generic way of instantiating instance of current class. Basically replace line #11 from:

  11: instance = MyCar(i)

to a more generic state which can be reused in any class. How can I do this ?

Answer 1

Use a class method, not a static method. That way, assuming for example that Bus inherits MyCar , then Bus.get_cars_from() will call the inherited MyCar.get_cars_from , but the cls argument will be set to Bus .

@classmethod
def get_cars_from(cls, start=0, end=10):
    """ This method get a list of cars from number 1 to 10.
    """
    return_list = []
    for i in range(start, end):
        instance = cls(i)
        return_list.append(instance)
    return return_list

Also, a list comprehension makes this a more-efficient one-liner:

@classmethod
def get_cars_from(cls, start=0, end=10):
    return [cls(i) for i in range(start, end)]

(but use xrange instead of range in Python 2).