[issue38131] compile(mode='eval') uninformative error message

[Batuhan Taskaya]

Batuhan Taskaya  added the comment:

I've updated PR 17715 in order to point out exact field that error happened. 
Also it now only shows type

>>> import ast
>>> expr_without_lineno_but_ok = 
>>> ast.Expression(body=ast.BinOp(left=ast.Num(n=2), right=ast.Num(n=2), 
>>> op=ast.Add()))
>>> expr_with_lineno_but_with_wrong_body = 
>>> ast.Expression(body=[ast.BinOp(left=ast.Num(n=2), right=ast.Num(n=2), 
>>> op=ast.Add())])
>>> ast.fix_missing_locations(expr_with_lineno_but_with_wrong_body)

>>> compile(expr_without_lineno_but_ok, "", "eval")
Traceback (most recent call last):
  File "", line 1, in 
TypeError: required field "lineno" missing from expr
>>> compile(expr_with_lineno_but_with_wrong_body, "", "eval")
Traceback (most recent call last):
  File "", line 1, in 
TypeError: For field 'body'; expected expr type node, got list

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[issue38131] compile(mode='eval') uninformative error message

[Batuhan Taskaya]

Change by Batuhan Taskaya :


--
nosy: +benjamin.peterson, pablogsal

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[issue38131] compile(mode='eval') uninformative error message

[Batuhan]

Change by Batuhan :


--
components: +Interpreter Core -Library (Lib)
nosy: +BTaskaya
versions: +Python 3.9 -Python 3.6, Python 3.7, Python 3.8

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[issue38131] compile(mode='eval') uninformative error message

[Batuhan]

Batuhan  added the comment:

with PR 17715 

>>> import ast
>>> expr_without_lineno_but_ok = 
>>> ast.Expression(body=ast.BinOp(left=ast.Num(n=2), right=ast.Num(n=2), 
>>> op=ast.Add()))
>>> expr_with_lineno_but_with_wrong_body = 
>>> ast.Expression(body=[ast.BinOp(left=ast.Num(n=2), right=ast.Num(n=2), 
>>> op=ast.Add())])
>>> ast.fix_missing_locations(expr_with_lineno_but_with_wrong_body)
>>> compile(expr_without_lineno_but_ok, "", "eval")
Traceback (most recent call last):
  File "", line 1, in 
TypeError: required field "lineno" missing from expr
>>> compile(expr_with_lineno_but_with_wrong_body, "", "eval")
Traceback (most recent call last):
  File "", line 1, in 
TypeError: expected some sort of expr, but got [<_ast.BinOp object at 
0x7f3f57dc4c80>]

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[issue38131] compile(mode='eval') uninformative error message

[Batuhan]

Change by Batuhan :


--
keywords: +patch
pull_requests: +17160
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/17715

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[issue38131] compile(mode='eval') uninformative error message

[Ilya Kamenshchikov]

New submission from Ilya Kamenshchikov :

While trying to construct a valid ast node programmatically, I have tried 
following: 

import ast

tree = ast.BinOp(left=ast.Num(n=2), right=ast.Num(n=2), op=ast.Add())
expr = ast.Expression(body=[tree])
ast.fix_missing_locations(expr)
exe = compile(expr, filename="", mode="eval")
print(eval(exe))

Unfortunately this gives unhelpful error message:

>>>exe = compile(expr, filename="", mode="eval")
TypeError: required field "lineno" missing from expr

Turns out I need to make body of ast.Expression not a list, but a node:
expr = ast.Expression(body=tree)  # works

Confusion also comes from naming the field "body", which takes value of a list 
for ast.Module and some others.

--
components: Library (Lib)
messages: 352090
nosy: Ilya Kamenshchikov
priority: normal
severity: normal
status: open
title: compile(mode='eval') uninformative error message
versions: Python 3.6, Python 3.7, Python 3.8

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