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.
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