Improve repr() of AST nodes

[JelleZijlstra]

Feature or enhancement

Proposal:

I often use ast.parse in the terminal to explore what the AST looks like:

>>> ast.parse("x = 3")
<ast.Module object at 0x105450b50>

But I have to remember to use ast.dump() to get useful output:

>>> ast.dump(ast.parse("x = 3"))
"Module(body=[Assign(targets=[Name(id='x', ctx=Store())], value=Constant(value=3))], type_ignores=[])"

It would be nice if the default repr() of AST nodes was more like the output of ast.dump(), so it's easier to see at a glance how it works.

One concern would be around the size of the output:

>>> from pathlib import Path
>>> import typing
>>> typing_py = Path(typing.__file__).read_text()
>>> len(ast.dump(ast.parse(typing_py)))
304244

As a middle ground, we could limit the depth of the AST provided in the repr(), e.g. to 2 levels, and also the number of list elements provided.

The repr() of a module's AST might then look something like:

Module(body=[Expr(value=Constant(...)), ..., Assign(targets=[Name(...)], value=Constant(...))], type_ignores=[])

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-116022: Improve repr() of AST nodes #117046

[tomasr8]

This is something that would be useful for me as well since I also sometimes poke around the AST 😄

Were you planning to implement this yourself or do you think I could give it a try? Looking at the code, it'll probably have to be implemented in C since that's where the base AST type is defined.

[JelleZijlstra]

I will do it eventually if no one else gets to it but haven't started yet. You're welcome to start working on it! This might need changes to asdl_c.py which is the Python code that generates the C code for the AST.