[issue35894] Apparent regression in 3.8-dev: 'TypeError: required field "type_ignores" missing from Module'

[Guido van Rossum]

Guido van Rossum  added the comment:

> [T]here's other optional fields in the ast, type ignores don't seem essential 
> to the `Module`, could those be made optional as well?

I think you're referring to the `?` syntax in `Python.asdl`.  But the 
`type_ignores` attribute is already a list (using `*`) and AFAICT you cannot 
combine `?` and `*`.  You have to provide an empty list.

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[issue35894] Apparent regression in 3.8-dev: 'TypeError: required field "type_ignores" missing from Module'

[David Lord]

Change by David Lord :


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nosy: +davidism

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[issue35894] Apparent regression in 3.8-dev: 'TypeError: required field "type_ignores" missing from Module'

[Anthony Sottile]

Anthony Sottile  added the comment:

there's other optional fields in the ast, type ignores don't seem essential to 
the `Module`, could those be made optional as well?

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nosy: +Anthony Sottile

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[issue35894] Apparent regression in 3.8-dev: 'TypeError: required field "type_ignores" missing from Module'

[Guido van Rossum]

Change by Guido van Rossum :


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resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue35894] Apparent regression in 3.8-dev: 'TypeError: required field "type_ignores" missing from Module'

[Nathaniel Smith]

Nathaniel Smith  added the comment:

Oh, that's not my code, it's the core of IPython's REPL :-). I just filed a bug 
with them, referencing this one: https://github.com/ipython/ipython/issues/11590

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[issue35894] Apparent regression in 3.8-dev: 'TypeError: required field "type_ignores" missing from Module'

[Guido van Rossum]

Guido van Rossum  added the comment:

Yeah, this definitely changed. When we updated typed_ast to Python 3.7 
recently, the mypy project looked into making certain arguments to AST certain 
nodes optional, but the code responsible for those arguments is too weird to 
easily make that work (it's all generated), so we decided to leave it alone.

IMO the AST in general can't be considered a stable API like other stdlib APIs, 
since when the syntax changes, well, the AST changes, and sometimes that means 
that nodes change. For *consumers* of the AST we generally manage to keep 
things backwards compatible, but for producers, there just is no guarantee.

I think the best way forward is for your code to check the Python version and 
if it's >= 3.8, pass an empty list as the second argument to Module().

If you look at the changes to Python.asdl in the PR you found, you'll see what 
other nodes have changed.

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[issue35894] Apparent regression in 3.8-dev: 'TypeError: required field "type_ignores" missing from Module'

[Nathaniel Smith]

New submission from Nathaniel Smith :

Travis provides a "3.8-dev" python, which is updated regularly to track cpython 
master. When running our tests on this Python, specifically version

  python: 3.8.0a0 (heads/master:f75d59e, Feb  3 2019, 07:27:24) 

we just started getting tracebacks:

  TypeError Traceback (most recent call last)
  /opt/python/3.8-dev/lib/python3.8/codeop.py in __call__(self, source, 
filename, symbol)
  131 
  132 def __call__(self, source, filename, symbol):
  --> 133 codeob = compile(source, filename, symbol, self.flags, 1)
  134 for feature in _features:
  135 if codeob.co_flags & feature.compiler_flag:
  TypeError: required field "type_ignores" missing from Module

(Full log: https://travis-ci.org/python-trio/trio/jobs/488312057)

Grepping through git diffs for 'type_ignores' suggests that this is probably 
related to bpo-35766.

I haven't dug into this in detail, but it seems to be happening on tests using 
IPython. The lack of further traceback suggests to me that the exception is 
happening inside IPython's guts (it has some hacks to try to figure out which 
parts of the traceback are in user-defined code versus its own internal code, 
and tries to hide the latter when printing tracebacks). The crash is in 
codeop.Compile.__call__, and IPython does create ast.Module objects and pass 
them to codeop.Compile.__call__:

https://github.com/ipython/ipython/blob/512d47340c09d184e20811ca46aaa2f862bcbafe/IPython/core/interactiveshell.py#L3199-L3200

Maybe ast.Module needs to default-initialize the new type_ignores field, or 
compile() needs to be tolerant of it being missing?

--
messages: 334807
nosy: benjamin.peterson, brett.cannon, gvanrossum, njs, yselivanov
priority: normal
severity: normal
status: open
title: Apparent regression in 3.8-dev: 'TypeError: required field 
"type_ignores" missing from Module'
type: behavior
versions: Python 3.8

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