Regular Expressions

Learning Objectives Define what a regular expression is and why it is useful. Identify and explain at least 5 common metacharacters (e.g., \d, \w, ., +, *). Use Python's `re.search()` function to find the first occurrence of a pattern in a string. Use Python's `re.findall()` function to extract all occurrences of a pattern from a string. Write a simple regular expression to validate a common data format, like a username or a zip code. Explain the difference between a literal character and a metacharacter in a regex pattern. Ever wondered how a website instantly knows if your email address is typed in the right format? 🤔 Let's learn the secret power of pattern matching! In this lesson, you'll learn about Regular Expressions, often called 'regex&#039...

TermDefinitionExample Regular Expression (Regex)A sequence of characters that defines a search pattern. It's used to check if a string contains the specified pattern.The pattern `\d+` is a regex that looks for one or more digits. PatternThe string that contains the regular expression rules.In `re.search('cat', 'the cat is cute')`, the pattern is 'cat'. Literal CharacterA character in a regex pattern that matches itself exactly.The pattern `abc` will only match the exact sequence of characters 'a', then 'b', then 'c'. MetacharacterA character with a special meaning in a regex pattern. It doesn't match itself.The metacharacter `.` matches any single character (except a newline). So, the pattern `c.t` would match 'cat...

Finding the First Match: `re.search()` re.search(pattern, string) Scans through a string looking for the first location where the regex pattern produces a match. If a match is found, it returns a special 'match object'; otherwise, it returns `None`. Finding All Matches: `re.findall()` re.findall(pattern, string) Finds all non-overlapping matches of the pattern in a string and returns them as a list of strings. If no matches are found, it returns an empty list. Common Metacharacter Shortcuts \d (any digit), \w (any letter, digit, or underscore), \s (any whitespace), . (any character), + (one or more), * (zero or more) These shortcuts make patterns shorter and more readable. For example, instead of writing `[0123456789]`, you can just write `\d`.