How to check if a Python string s1 contains another string s2? There are two easy ways to check whether string s1 contains string s2: Use the expression s2 in s1, or Use the find method s1.find(s2). You can try both methods in our interactive Python shell (just click “Run” to execute the code in …
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 …
The Dot Character in a Character Set – What Does It Match? 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() …
Python Lists filter() vs List Comprehension – Which is Faster? Read More »
How can you filter a list in Python using an arbitrary condition? The most Pythonic and most performant way is to use list comprehension [x for x in list if condition] to filter all elements from a list. Try It Yourself: Filter with List Comprehension The most Pythonic way of filtering a list—in my opinion—is …
Today, I stumbled upon this beautiful regex problem: Given is a multi-line string and a regex pattern. How to find all lines that do NOT contain the regex pattern? I’ll give you a short answer and a long answer. The short answer is to use the pattern ‘((?!regex).)*’ to match all lines that do not …
How to Find All Lines Not Containing a Regex in Python? Read More »
This morning, I read over an actual Quora thread with this precise question. While there’s no dumb question, the question reveals that there may be some gap in understanding the basics in Python and Python’s regular expression library. So if you’re an impatient person, here’s the short answer: How to match an exact word/string using …
How to Match an Exact Word in Python Regex? (Answer: Don’t) Read More »
Regular expressions are a strange animal. Many students find them difficult to understand – do you? I realized that a major reason for this is simply that they don’t understand the special regex characters. To put it differently: understand the special characters and everything else in the regex space will come much easier to you. …
Regex Special Characters – Examples in Python Re Read More »
This tutorial explains everything you need to know about matching groups in Python’s re package for regular expressions. You may have also read the term “capture groups” which points to the same concept. As you read through the tutorial, you can also watch the tutorial video where I explain everything in a simple way: Related …
Ready to earn the black belt of your regex superpower? This tutorial shows you the subtle but important difference between greedy and non-greedy regex quantifiers. You can also watch the explainer video I created for this article: If you’re a busy person, here’s the short version of this tutorial: Definition Greedy Quantifier: A greedy quantifier …
This tutorial makes you a master of character sets in Python. (I know, I know, it feels awesome to see your deepest desires finally come true.) As I wrote this article, I saw a lot of different terms describing this same powerful concept such as “character class“, “character range“, or “character group“. However, the most …
A regular expression is a decades-old concept in computer science. Invented in the 1950s by famous mathematician Stephen Cole Kleene, the decades of evolution brought a huge variety of operations. Collecting all operations and writing up a comprehensive list would result in a very thick and unreadable book by itself. Related article: Python Regex Superpower …
What’s the best-kept productivity secret of code masters? Here’s what ex-Google’s tech lead says is the most important skill as a coder (spoiler: it has to do with the topic of the tutorial): Congratulations – you’re about to become a regular expression master. I’ve not only written the most comprehensive free regular expression tutorial on …