compile(mode='eval') uninformative error message #82312

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1. ikamensh commented on Sep 12, 2019

   

   ikamenshmannequin

   on Sep 12, 2019

   MannequinAuthor

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   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.
2. ikamensh

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   3.7 (EOL)end of lifeend of life

   3.8 (EOL)end of lifeend of life

   on Sep 12, 2019
3. isidentical

   added

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   3.9 (EOL)end of lifeend of life

   and removed

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   3.7 (EOL)end of lifeend of life

   3.8 (EOL)end of lifeend of life

   on Dec 27, 2019
4. isidentical commented on Dec 27, 2019

   

   isidentical

   on Dec 27, 2019

   SponsorMember

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   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, "<temp>", "eval")
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: required field "lineno" missing from expr
   >>> compile(expr_with_lineno_but_with_wrong_body, "<temp>", "eval")
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: expected some sort of expr, but got [<_ast.BinOp object at 0x7f3f57dc4c80>]
5. isidentical commented on May 7, 2020

   

   isidentical

   on May 7, 2020

   SponsorMember

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   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)
   <ast.Expression object at 0x7f854123fbb0>
   >>> compile(expr_without_lineno_but_ok, "<temp>", "eval")
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: required field "lineno" missing from expr
   >>> compile(expr_with_lineno_but_with_wrong_body, "<temp>", "eval")
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: For field 'body'; expected expr type node, got list
6. ezio-melotti

   transferred this issue fromon Apr 10, 2022
7. StanFromIreland

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8. serhiy-storchaka

   added a commit that references this issue on Jun 29, 2026

   gh-82312: Further improvement of error messages for generating AST no…

   ...

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