Let's take a look at a function from the Python docs for calculating the n th Fibonacci number. Obviously we probably wouldn't want to only have the first 10 Fibonacci numbers in an object. So although this is a very contrived example, hopefully this demonstrates the ability for us to customize the behavior of our code. Raise TypeError("Not allowed to modify the Fibonacci Numbers") But we can implement the method and add a custom error message if someone tries to set values in the way discussed above. In our case we probably don't want to be able to be able to allow setting the Fibonacci numbers, but clearly in many cases we will want it. Recall that with normal lists in Python we can set an element in a list using the following syntax:īehind the scenes Python is using the following: Since we have the _len_ method defined in our class we can also loop through all the elements using a common looping technique. We also implement the _len_ method to allow us to call the len() keyword on an instance of our object. First let's see how this method works with Python's built in list objects. Therefore if we want to be able to access elements in the typical way there are a few methods we will need to implement.īelow we define a _getitem_ method which returns the elements based on the given slice_ we pass through to the method. If you ever see the TypeError: object is not subscriptable exception , the reason why is that a special method has not be included in the class. TypeError: 'Fib10' object is not subscriptable Trying this with an instance of our Fib10 class results in the following: Say we wanted to be able to access the elements within this class the way we typically do with lists in Python. Let's begin with a simple object that contains the first 10 Fibonacci numbers. In this article we will focus on lists and generators, however the same methods can be used for dictionaries.įirst recall how we usually access elements of a list in Python mylist = We will use the Fibonacci sequence to demonstrate these concepts, since they are also quite a popular interview question, hopefully this will make these concepts easy to remember. This article will give an overview on how to use them. Sequences are quite possibly the most widely used data structure in programming. ) and any generator is also an iterable.Python Sequence Objects with Fibonacci Example An iterable is anything you can iterate (e.g. The next function is the built-in function that requests the next value from the iterable. Here is a quick self-explanationary example: > def example(): As the generator stops, it won’t hang up despite that loop. As you see in the definition of fibGenerator above, there is a endless while-loop which has a yield inside. Using a generator allows you to create an endless sequence. The next time you request a value, the generator will continue where it left off. A yield will “return” a value and pause the generator. You create a generator by simply using yield instead of return. The values are generated lazily, that means when you request it. Still not too sure what the generator does however.Ī generator is a Python function which generates a sequence of return values. Instead of iterating over a range and calling next on the generator manually, you then can also just use the take-recipe from itertools to do it just like this: fibonaccinumbers = take(20, fibGenerator()) You can also use a generator function to make that all easier: def fibGenerator(): That way you don’t have to do the same things over and over again. You should define it outside of it and just reuse it.Īlso, when you know you want to create a list of multiple fibonacci numbers, it helps to just store all the numbers you calculate in between. Then you are redefinining your fib function inside the loop over and over again. Also, you can simplify the whole block by just doing this: numberlist = list(range(20))Īnd given that you don’t actually need that to be a list, you don’t need to construct that at all but you can just run for n in range(20) later. You don’t need to initialize i there, the for loop does that for you. Also some more comments on your code: numberlist =
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