![]() I encourage you to play with this article’s examples and modify them. This article explored how to decrement in a for loop using Python’s built-in methods. If you are interested in Python data structures (and you should be), I again encourage you to read this article on arrays and lists in Python, where you will also learn about NumPy, one of the best Python libraries for working with arrays. ![]() using a while loop or list properties – but I won’t cover them here. There are also other ways to decrement in Python – e.g. Of course, you can always reverse it again. So if you want to keep the original list unchanged, you should use reversed(). We won’t need to use the reversed() function any more in the for loop, but the list will stay reversed. On the other hand, if we use the reverse() method, we will modify the list. In other words, if we print the variable a, we get the same initial list. However, it is essential to note that the reversed() function does not modify the list. Let's try with a simple list of numbers:Īnd our list is printed in reversed order. Therefore, if we want to decrement a Python for loop, we can wrap a list with the reversed() function. The Python reversed() function will reverse a list without modifying it. Decrementing a Python for Loop with reverse() and reversed() If you find this confusing, you can read more about arrays and lists in Python.Īnother way to decrement is to use the Python reversed() method. Next, we need to set the end parameter to -1 because we want to stop at the first element, which has the index value of 0. Similarly, you can also return "f" by typing a. For example, if I want to output "f" from the list above, I need to input a. While "f" is effectively the sixth element of the above list, its index is 5. In list a, we want to start decrementing from "f". (However, it’s good to note that the R and MATLAB programming languages start from 1.) It is important to define the start parameter as len(a) - 1 because in Python (and computer sciences in general) we start counting from 0. If you don’t remember lists and other Python data structures, I encourage you to read more about the difference between lists, tuples, and dictionaries before you continue. We can also define a list of elements and display them in reverse order based on the list length. Let's modify the previous example and output the results: We can also set the step parameter to some other value (like -3) and the for loop will decrement by 3 instead of 1. Finally, step=-1 because it’s the difference between each number we would like to get and the previous one (e.g., 8 - 9 = -1, 2 - 3 = -1, etc.) The end is set to -1 because the end value is always excluded here, the last value we want to print is 0. The start parameter is set to 9 because that is the first value we want to obtain. We can apply it in a straightforward manner by setting the start and the end parameters so that end > for i in range(9, -1, -1):Īnd here we go! We have exactly the same loop as above, but in reverse order. The previous example provides some insight on how to decrement in a Python for loop using range(). Decrementing a Python for Loop with range() Next, let’s explore how to use this knowledge to decrement a Python for loop. ![]() The above syntax is equivalent to writing: The start and step parameters are optional they default to 0 and 1, respectively. If we only specify one value, by default it is the end parameter. As per the Python documentation, its syntax is as follows: If you do not know, maybe it is because you are not familiar with the complete syntax of the range() method. We just incremented successfully! But how do we decrement? In other words, how can we print 9, 8, 7, 6, 5, 4, 3, 2, 1, 0? You might have already learned this common way of implementing a for loop in Python: Okay, on to the for loop! Incrementing a Python for Loop And if you’re taking your first steps in Python – or you just want to practice what you already know – we have a set of 5 interactive courses covering Python basic commands, data structures, and built-in algorithms in138 coding challenges. If you need a refresher on the Python for loop, read Kateryna's article on writing for loops in Python, then come back here. In Python, we state the beginning and the end of the iteration with the number of steps in between. Unlike other programming languages (such as C++) Python has no decrement operator (i.e. Do you know how to decrement in Python? It’s easy! You can do it with a simple for loop, and I’ll show you how.
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