[Python-Dev] Recent experience with the _ast module

["Martin v. Löwis"]

Collin Winter schrieb:
> 1) There are times when the _fields attribute on some AST nodes is
> None; if this was done to indicate that a given node has no
> AST-related attributes, it would be much easier if _fields was [] in
> this case. As it is, I had to special-case "node._fields is None" in
> the visitor so that I don't accidentally iterate over it.

That can be done, I think.

> 2) {BinOp,AugAssign,BoolOp,etc}.op is an instance of, eg, Add, Sub,
> Mult, Mod, meaning you have to dispatch based on tests like
> "isinstance(node.op, x)" or "type(node.op) is x". I would much, much
> prefer to spell this "node.op is x", ie, use "node.op = Add" rather
> than the current "node.op = Add()" when constructing the nodes.

Please look at Python.asdl. This things are really belong to sum nodes,
and Add, Sub etc. are really operators.

I *think* they are singletons, and I don't mind making it a guarantee
that they are: i.e. all operators that have no fields and where the
sum has no attributes.

If you want to write "is", you can also write

    node.op.__class__ is Add

> 3) I'd like there to be an Else() node for If.orelse, While.orelse,
> etc. My motivation is that I need the lineno and col_offset values of
> the "else" statement for a code-coverage utility; as it is, I have to
> find the last lineno of the if/while/etc suite and the first lineno of
> the "else" suite and then search between those two for the "else"
> statement.

Notice that you cannot restore the original source code, anyway. You
cannot tell whether something was else:if or elif.

I don't understand why you need the line number of the else keyword
(which, as I said, may not exist in the source) for code coverage:
The 'else' is never executed (only the statements in it are).

Regards,
Martin