What is a regular expression used for?

A regular expression, commonly referred to as regex, is primarily used to execute search patterns on text. It serves as a powerful tool for manipulating strings, allowing users to search, match, and manipulate text based on specific patterns or sequences of characters. Regular expressions can be employed for various tasks such as validating input formats (e.g., email addresses, phone numbers), searching for specific patterns within a body of text, and performing replacements across text data.

The other options involve different concepts within data science and machine learning. Defining machine learning models pertains to selecting algorithms and constructing the framework for predictive analytics, which does not involve regex. Optimizing hyperparameters is a process focused on tweaking model parameters to improve performance, which requires methods distinct from text pattern matching. Evaluating model performance involves measuring outcomes against metrics like accuracy or F1-score, again relying on statistical methods rather than text-based pattern recognition. Therefore, regex is evidently specialized for text searching and manipulation, making it a crucial tool in data preprocessing and textual analysis.