Add Transformer API for in-place manipulation of AST

[Pike]

Also, deprecate .traverse.

[stasm]

Nice work!

[stasm]

I think I liked the split between visit and visit_node, but it's perfectly fine to combine them into a single method. I guess this is done for symmetry with Transformer.visit? Also, nit: rename value to node?

[Pike]

Right, and also to follow the pattern of ast more closely. What really bothered me was that Transformer subclasses Visitor (for reasons I find odd but didn't debate), and thus had visit_node, but couldn't use it, really.

[stasm]

I remember that at some point we add a tuple check here: cf564c3. I think the goal was to support Annotations' args field which is a tuple.

We should probably fix it in

python-fluent/fluent.syntax/fluent/syntax/errors.py

Lines 4 to 8 in f3f9053

	class ParseError(Exception):
	def __init__(self, code, *args):
	self.code = code
	self.args = args
	self.message = get_error_message(code, args)

, but perhaps it's safer to added the check here first?

[Pike]

Mind blown.

https://github.com/python/cpython/blob/cfd31f0af20f76849bbec6185efea01c72349f2a/Objects/exceptions.c#L202

You cannot un-tuple .args.