ast.parse

Learn to build an AST with ast.parse.

What is ast.parse?

ast.parse turns a source code string into an abstract syntax tree (AST). Each node in the tree represents a syntax element: a statement, an expression, a name, a constant.

For example ast.parse("x = 1 + 2") returns a Module node; its .body list contains an Assign statement. You can walk and analyse this tree, transform it or recompile it. ASTs are the foundation of linters, code generators and teaching tools.

AST nodes

AST nodes are defined as classes in the ast module. Assign is for assignment, BinOp for binary operations, Name for variable names, Constant for literal values.

You can learn a node's type with type(node).__name__. You access sub-fields with a dot: node.targets, node.value. To understand the tree ast.dump(tree) shows the full structure as a string. This is very handy for debugging.

Exercise Build a tree with ast.parse

Import the module with import ast. Build the tree with ast.parse("x = 1 + 2"). Get the first statement with tree.body[0]. Print the node type name with type(node).__name__.

Show example solution

import ast

tree = ast.parse("x = 1 + 2")
node = tree.body[0]
print(type(node).__name__)

Test yourself

What does ast.parse return?
```
import ast
tree = ast.parse("x = 1")
```
- A list
- A string
- A Module node
- An error
Show answer

A Module node — ast.parse returns a Module node; .body lists the statements.

Complete the ast.parse call

tree = ____("x = 1 + 2")

Show answer

tree = ast.parse("x = 1 + 2")

Match AST concepts

ast.parse

Parses code into a tree
Module

Root node
body

Statement list
Assign

Assignment statement

Next lesson: ast.walk

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