[New-bugs-announce] [issue46078] `ast.unparse` fails on `class C: i: int`… convert broken from `ast.AnnAssign` to `ast.Assign`
Samuel Marks
report at bugs.python.org
Tue Dec 14 21:37:47 EST 2021
New submission from Samuel Marks <samuelmarks at gmail.com>:
astor fails with:
```
File "python3.8/site-packages/astor/code_gen.py", line 63, in to_source
generator.visit(node)
File "python3.8/site-packages/astor/node_util.py", line 143, in visit
return visitor(node)
File "python3.8/site-packages/astor/code_gen.py", line 878, in visit_Module
self.write(*node.body)
File "python3.8/site-packages/astor/code_gen.py", line 178, in write
visit(item)
File "python3.8/site-packages/astor/node_util.py", line 143, in visit
return visitor(node)
File "python3.8/site-packages/astor/code_gen.py", line 364, in visit_ClassDef
self.body(node.body)
File "python3.8/site-packages/astor/code_gen.py", line 226, in body
self.write(*statements)
File "python3.8/site-packages/astor/code_gen.py", line 178, in write
visit(item)
File "python3.8/site-packages/astor/node_util.py", line 143, in visit
return visitor(node)
File "python3.8/site-packages/astor/code_gen.py", line 293, in visit_Assign
self.visit(node.value)
File "python3.8/site-packages/astor/node_util.py", line 143, in visit
return visitor(node)
File "python3.8/site-packages/astor/node_util.py", line 137, in abort_visit
raise AttributeError(msg % node.__class__.__name__)
AttributeError: No defined handler for node of type NoneType
```
Whereas the now builtin to Python (3.9+) `ast.unparse` gives:
```
File "3.10/lib/python3.10/ast.py", line 1673, in unparse
return unparser.visit(ast_obj)
File "3.10/lib/python3.10/ast.py", line 807, in visit
self.traverse(node)
File "3.10/lib/python3.10/ast.py", line 798, in traverse
super().visit(node)
File "3.10/lib/python3.10/ast.py", line 410, in visit
return visitor(node)
File "3.10/lib/python3.10/ast.py", line 822, in visit_Module
self._write_docstring_and_traverse_body(node)
File "3.10/lib/python3.10/ast.py", line 815, in _write_docstring_and_traverse_body
self.traverse(node.body)
File "3.10/lib/python3.10/ast.py", line 796, in traverse
self.traverse(item)
File "3.10/lib/python3.10/ast.py", line 798, in traverse
super().visit(node)
File "3.10/lib/python3.10/ast.py", line 410, in visit
return visitor(node)
File "3.10/lib/python3.10/ast.py", line 1001, in visit_ClassDef
self._write_docstring_and_traverse_body(node)
File "3.10/lib/python3.10/ast.py", line 815, in _write_docstring_and_traverse_body
self.traverse(node.body)
File "3.10/lib/python3.10/ast.py", line 796, in traverse
self.traverse(item)
File "3.10/lib/python3.10/ast.py", line 798, in traverse
super().visit(node)
File "3.10/lib/python3.10/ast.py", line 410, in visit
return visitor(node)
File "3.10/lib/python3.10/ast.py", line 863, in visit_Assign
self.traverse(node.value)
File "3.10/lib/python3.10/ast.py", line 798, in traverse
super().visit(node)
File "3.10/lib/python3.10/ast.py", line 410, in visit
return visitor(node)
File "3.10/lib/python3.10/ast.py", line 414, in generic_visit
for field, value in iter_fields(node):
File "3.10/lib/python3.10/ast.py", line 252, in iter_fields
for field in node._fields:
AttributeError: 'NoneType' object has no attribute '_fields'
```
Found it when I tried to unparse previously parsed:
```py
class C:
i: int
```
Found in reality when trying to parse then emit:
- https://github.com/tensorflow/tensorflow/blob/ba146843/tensorflow/compiler/xla/python/xla_client.py#L402-L413
Which is creating this:
```
ast.Assign(targets=[ast.Name(id="interior_padding")],
type_comment="int",
value=None)
```
(one thing my library does is convert betwixt `ast.Assign` and `ast.AnnAssign`… later I'll be doing more interesting variable type tracing to generate big `typing.Union` of all possible types each variable may have… but if it finds `None` then it will infer `typing.Optional`.)
Here is my `ast.NodeTransformer` override for `visit_AnnAssign`: https://github.com/offscale/cdd-python/blob/968507e/cdd/doctrans_utils.py#L111-L131
Is there some way of rewriting an `ast.AnnAssign` to `ast.Assign` without losing type information?
----------
messages: 408580
nosy: samuelmarks
priority: normal
severity: normal
status: open
title: `ast.unparse` fails on `class C: i: int`… convert broken from `ast.AnnAssign` to `ast.Assign`
versions: Python 3.10, Python 3.11, Python 3.8, Python 3.9
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<https://bugs.python.org/issue46078>
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