Learn more about the special function len(self) in python

May 23, 2017 pm 02:49 PM

len If a class behaves like a list, to get the number of elements, you have to use the len() function. For the len() function to work properly, the class must provide a special method len(), which returns the number of elements.
For example, we write a Students class and pass the name in:

1 2	`class` `Students(object): def init(self, *args):` `self.names = args def len(self):` `return` `len(self.names)`

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As long as the len() method is correctly implemented, you can use the len() function to return the "length" of the Students instance:

1	`>>> ss = Students('Bob', 'Alice', 'Tim')>>>` `print` `len(ss)3`

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Task
The Fibonacci sequence is composed of 0, 1, 1, 2, 3, 5, 8....
Please write a Fib class. Fib(10) represents the first 10 elements of the sequence. print Fib(10) can print out the first 10 elements of the sequence. len(Fib(10)) can correctly return the number of the sequence. 10.

Need to calculate the first N elements of the Fibonacci sequence based on num.
Reference code:

class Fib(object):    def init(self, num):
        a, b, L = 0, 1, []        for n in range(num):
            L.append(a)
            a, b = b, a + b
        self.numbers = L    def str(self):        return str(self.numbers)    repr = str
    def len(self):        return len(self.numbers)
f = Fib(10)print fprint len(f)

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List can only insert elements through append and insert! ! !

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