Pattern matching

Find the first occurrence of a regex pattern within a text string.

Data cleaning: Validating user input against a format Web scraping: Extracting data from logs or structured text Input validation: Parsing strings for specific substrings defined by a pattern

Data cleaning and transformation pipelines Web scraping and HTML/XML parsing Input validation in web forms or APIs

re.search(pattern, string)

re.search(...)

pattern: regex string (raw string recommended), string: input text to be searched

• re.match re.findall re.sub re.compile match.group()

• re.match for start‑of‑string anchored searches re.findall to retrieve all non‑overlapping matches re.finditer for iterator‑based traversal

Assuming re.search returns -1 on failure (it returns None) Accessing .group() on a None result causing AttributeError Forgetting to use raw strings, leading to unintended escape sequences

re.match – matches only at the beginning of the string; re.search scans the whole string re.fullmatch – requires the entire string to conform to the pattern

Coming from languages with indexOf‑style searches: expecting a numeric index or -1, but re.search returns a match object or None From JavaScript: confusing RegExp.test() (boolean) with Python’s match object

• re.match
• re.findall
• re.finditer
• re.split
• re.sub

The match object provides .group(), .start(), .end(), and .span() to extract details; using a raw string (r'...') avoids double‑escaping backslashes in the pattern.

Allows concise, declarative extraction of substrings without manual looping or character‑by‑character checks.

Search for pattern anywhere – think ‘re.search finds the first hit’.

re.search scans a string for the first regex match, returning a match object or None if no match is found.

Pre‑compile the pattern with re.compile for repeated searches: pattern_obj = re.compile(pattern); pattern_obj.search(string)