ChrisSay, you want to convert a list of lists lst=[[1, 2], [3, 4]] into a single list [1, 2, 3, 4]. How to achieve this? There are different options: List comprehension [x for l in lst for x in l] assuming you have a list of lists lst. Unpacking [*lst[0], *lst[1]] assuming you have a … Read more
There’s an element of confusion regarding the term “lists of lists” in Python. I wrote this most comprehensive tutorial on list of lists in the world to remove all those confusions by beginners in the Python programming language. This multi-modal tutorial consists of: Source code to copy&paste in your own projects. Interactive code you can … Read more
Problem: Given a Python list with n elements. How to convert it into a tuple with the same n elements? Examples: Note Tuple: Tuples are similar to lists—with the difference that you cannot change the tuple values (tuples are immutable) and you use parentheses rather than square brackets. Solution: Use the built-in Python tuple() function … Read more
Summing up a list of numbers appears everywhere in coding. Fortunately, Python provides the built-in sum() function to sum over all elements in a Python list—or any other iterable for that matter. (Official Docs) The syntax is sum(iterable, start=0): Argument Description iterable Sum over all elements in the iterable. This can be a list, a … Read more
How to print a Python list in a beautiful and fully customizable way? This article shows you six effective ways of doing it. By studying these alternatives, you’ll not only learn how to print lists in Python, you’ll become a better coder overall. If you just want to know the best way to print a … Read more
Given is the following regular expression: Note the dot character inside the character set. As you may know, the dot metacharacter matches an arbitrary character if it is used outside a character set. But what does it match if you place the dot character inside a regex character set? The answer is that the dot … Read more
To get the number of elements in a Python list, use the len(list) function. You don’t need to import any external library because len() is a Python built-in function. You can use it to get the number of elements of several built-in and library types in Python such as tuples and sets. Here’s the minimal … Read more
Do you know the best way of removing duplicates from a Python list? This is a popular coding interview question at Google, Facebook, and Amazon. In this article, I’ll show you how (and why) it works—so keep reading! How to remove all duplicates of a given value in the list? Naive Method: Go over each … Read more
When does the IndexError: list assignment index out of range appear? Python throws an IndexError if you try to assign a value to a list index that doesn’t exist, yet. For example, if you execute the expression list[1] = 10 on an empty list, Python throws the IndexError. Simply resolve it by adding elements to … Read more
Problem: Given a list of strings. How to convert the list to a string by concatenating all strings in the list? Example: You want to convert list [‘learn ‘, ‘python ‘, ‘fast’] to the string ‘learn python fast’. Solution: to convert a list of strings to a string, do the following. Call the ”.join(list) method … Read more
[Spoiler] Which function filters a list faster: filter() vs list comprehension? For large lists with one million elements, filtering lists with list comprehension is 40% faster than the built-in filter() method. To answer this question, I’ve written a short script that tests the runtime performance of filtering large lists of increasing sizes using the filter() … Read more
Nested List Comprehension—what does it even mean? There are three equally interpretations of this term: Coming from a computer science background, I was assuming that “nested list comprehension” refers to the creation of a list of lists. In other words: How to create a nested list with list comprehension? But after a bit of research, … Read more