Converting AST to text

[Alex Hall]

The section Going backwards says:

Python itself doesn’t provide a way to turn a compiled code object into an AST, or an AST into a string of code.

Python 3.9 added ast.unparse which converts an AST node to a string:

>>> ast.unparse(ast.parse("x = 1 + 2"))
'\nx = 1 + 2'

Python 3.8 added get_source_segment which gives the original source code of a specific node using line numbers and column offsets and the full source code:

>>> source = "x = 1 + 2"
>>> tree = ast.parse(source)
>>> tree.body[0].value
<ast.BinOp object at 0x10c8bf160>
>>> ast.get_source_segment(source, tree.body[0].value)
'1 + 2'

asttokens is a great project which can do the work of get_source_segment for older versions, back to Python 2.7. I have used it for many projects of my own.

[Thomas Kluyver]

We should definitely mention unparse once it’s nearing release.

I’m open to also pointing people to get_source_segment and asttokens, but they should be clearly distinguished. If I understand correctly, they’re looking back at code that was parsed, so you can’t use them to turn a generated or modified AST into code.