python / python/cpython

incorrect source ranges for `not a in b`

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#137,843 3 comments 0 reactions 1 assignee View on GitHub

@Eclips4 is already working on this.

Since May 31, 2026.

3.14 3.15 interpreter-core type-bug
Dominant language
Python
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Description

Bug report

Bug description:

python includes the not in the source ranges with 3.14.0-rc2.

class C:
    def __contains__(self, other):
        assert False


print(not 1 in C())

output (Python 3.14.0rc2+):

Traceback (most recent call last):
  File "/home/frank/projects/executing/example.py", line 6, in <module>
    print(not 1 in C())
          ^^^^^^^^^^^^
  File "/home/frank/projects/executing/example.py", line 3, in __contains__
    assert False
           ^^^^^
AssertionError

This was not the case in 3.13

output (Python 3.13.1):

Traceback (most recent call last):
  File "/home/frank/projects/executing/example.py", line 6, in <module>
    print(not 1 in C())
              ^^^^^^^^
  File "/home/frank/projects/executing/example.py", line 3, in __contains__
    assert False
           ^^^^^
AssertionError

I bisected the problem down to 38642bff139bde5c0118bc75fda25badc76b85fc @WolframAlph maybe you want to take a look at it?

This was the test which I used to bisect the problem:

import dis

for inst in dis.Bytecode(compile("not a in b","","exec")):
    if inst.opname=="CONTAINS_OP":
        assert inst.positions.col_offset==4
CPython versions tested on:

3.14, 3.15, CPython main branch

Operating systems tested on:

No response

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