Builtin eval() function raises NameError on a valid expression:


--- example of bug on Python 3.4
Python 3.4.5 (default, May 29 2017, 15:17:55)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-11)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> x = [1,2,3]
>>> [x for i in x]
[[1, 2, 3], [1, 2, 3], [1, 2, 3]]
>>> eval('[x for i in x]', {}, dict(x=x))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1, in <module>
  File "<string>", line 1, in <listcomp>
NameError: name 'x' is not defined


--- example on Python 2.7 (no bug)
Python 2.7.5 (default, May  3 2017, 07:55:04)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-14)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> x = [1,2,3]
>>> [x for i in x]
[[1, 2, 3], [1, 2, 3], [1, 2, 3]]
>>> eval('[x for i in x]', {}, dict(x=x))
[[1, 2, 3], [1, 2, 3], [1, 2, 3]]


---

Bug reproduced on:
- Windows 7: Python 3.4, 3.7
- Red Hat Enterprise Linux Server: Python 3.4

Works without errors on:
- Windows 7: Python 2.7
- Red Hat Enterprise Linux Server: Python 2.7

I believe you're seeing this: https://docs.python.org/3/reference/executionmodel.html#naming-and-binding

See the paragraph that starts with "Class definition blocks and arguments to exec() and eval() are special in the context of name resolution", and the example that follows it.

Basically, you're running eval() as if it were at class scope. I think (but am not positive) that this statement, from the exec() documentation, also applies to eval(): "Remember that at module level, globals and locals are the same dictionary. If exec gets two separate objects as globals and locals, the code will be executed as if it were embedded in a class definition."

If so, then eval()'s docs should reference this, too.

Eric, thank you for the clarification. Do you want me to close the ticket?

I'll close this. I'm still reviewing the docs on it, and I might open a documentation issue once I understand it better.