Problem: Given the contents of a text file. How to search and replace a specific string or line in the file? Example: Let’s consider the following example. Text in the file before replacing a line: There was an idea to bring together a group of remarkable people to see if we could become something more. …
How to Search and Replace a Line in a File in Python? Read More »
Summary: To match a pattern in a given text using only a single line of Python code, use the one-liner import re; print(re.findall(pattern, text)) that imports the regular expression library re and prints the result of the findall() function to the shell. Problem: Given a string and a regular expression pattern. Match the string for …
This is a running document in which I’ll answer all questions regarding the single line of Python code. If you want to become a one-liner wizard, check out my book “Python One-Liners”! 🙂 This document contains many interactive code shells and videos to help you with your understanding. However, it’s pretty slow because of all …
The standard way of checking if an element exists in a list is to use the in keyword. For example, ‘Alice’ in [1, ‘Alice’, 3] will return True while the same returns False for ‘Bob’. If you need to check more complicated conditions, use the any(condition(x) for x in list) function with a generator expression. …
The Most Pythonic Way to Check If a List Contains an Element Read More »
Yes, the dot regex matches whitespace characters when using Python’s re module. Consider the following example: Try it yourself in our interactive Python shell (click “run”): The dot matches all characters in the string–including whitespaces. You can see that there are many whitespace characters ‘ ‘ among the matched characters. Need more info? Watch the …
Does the Dot Regex (.) Match Whitespace Characters in Python? Read More »
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. Filter with List Comprehension The most Pythonic way of filtering a list—in my opinion—is the list comprehension …
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 »
The web is full of tutorials about regular expressions. But I realized that most of those tutorials lack a thorough motivation. Why do regular expressions exist? What are they used for? What are some practical applications? Somehow, the writers of those tutorials believe that readers are motivated by default to learn a technology that’s complicated …
What are Regular Expressions Used For? 10 Applications Read More »