I'll create a ticket shortly containing my local branch so far. (The
phase refactorings I've posted earlier is *not* included, this is all
useful stuff :-) ).
If anybody wants to start a process of applying it or discuss it then
fine, but there's no hurry, if nothing happens I'll just ping the list
again when Robert has more time available.
A summary:
I'll get to the main feature first so that you have a reason for
applying this :-) It should now be possible to do stuff like:
class WithTransform(VisitorTransform):
# from with transform PEP...
with_fragment = TreeFragment(u"""
_mgr = (EXPR)
_exit = mgr.__exit__
_value = mgr.__enter__()
_exc = True
try:
try:
VAR = _value
BLOCK
...
<snip>
...
""")
def process_WithStatementNode(self, node):
return self.with_fragment.substitute({
"EXPR" : node.expr,
"VAR" : node.var,
"BLOCK" : node.body
})
:-)
(The above is simplified, there's not always a VAR. Also it needs
another feature before it can be completely streamlined (automatic
"temporaries" that won't clash in the namespace; basically,
"with_fragment.substitute(..., temps=("_mgr", ...)). When that is done,
supporting the with statement is about as much work as extending the
parser, the transform/implementation comes for free.
- I've already discussed the CodeWriter. It only supports a limited
subset (with some holes, ~30% perhaps) at this time; but it's what I
need for now (for unit tests). I might work further on that too.
- Some changes to Transform.py which I hope goes through... there's a
Visitor object there; using the "process_ClassName" pattern (I think
that was the conclusion for future performance reasons).
- A clone_node method on Node for proper node copying (shallow object
copy except child node lists, which are also copied).
- Here's the controversial bit:
In order to be able to provide proper error messages for string-based
code snippets like the above (which are passed to Parsing.py...); I've
changed the pointer to the source code (used as the first element in the
position tuples found everywhere...) from being a string filename to
being a SourceDescriptor object.
A SourceDescriptor can currently be a FileSourceDescriptor, in which
case things work like before (it gives the filename on __str__ so much
code needed not change), or a StringSourceDestriptor which I use for my
new code...
I hope you see the advantages to this from the above code. (There are
less intrusive ways to do this, but they would only be hacky and
postpone the problem. Better do it properly...? BTW this pattern is
rather common, consider for instance Source in the XML Transform APIs/TrAX.)
--
Dag Sverre
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