Can you explain what an abstract syntax tree is and how it is used in source code processing?

An Abstract Syntax Tree (AST) is a tree data structure that represents the syntactic structure of source code. Each node of the tree corresponds to a construct of the programming language, such as an expression, operator, variable declaration, etc.

AST is used during compilation or interpretation phases for analyzing and transforming code. Instead of working with raw source text, tools operate on the AST, which simplifies syntax checking, optimization, and code generation for machine code or bytecode.

In Python, the ast module allows parsing source code into an AST and analyzing it, for example:

import ast

source = "a = 1 + 2"
parsed = ast.parse(source)
print(ast.dump(parsed, indent=4))

This outputs the tree structure, showing that the assignment consists of a variable name and an addition expression.