Pattern matching

Pattern matching, introduced in Python 3.10 via PEP 634, is a control structure that compares a value against patterns and executes the matching branch. It uses the match and case keywords. Patterns can match literals, types, sequences, mappings, classes, and combinations.

Match supports structural patterns that destructure data and bind variables in one step. It can match the shape of a class instance, the contents of a sequence, or the keys of a dictionary. This is more concise and expressive than equivalent if-elif chains, especially for parsing structured data.

A guard is an extra condition added to a case using if. The case matches only if both the pattern matches and the guard is true. Guards are useful when a structural pattern matches the shape but additional conditions on the values are needed.

A class pattern matches an instance of a class and optionally extracts attributes. The syntax uses the class name followed by parentheses with attribute patterns. Class patterns can use positional sub-patterns through the dunder match args attribute. They are powerful for working with data classes and ASTs. ---