# Has sys.setrecursionlimit() behaviour changed in Python 3.12b?

**URL:** <https://discuss.python.org/t/has-sys-setrecursionlimit-behaviour-changed-in-python-3-12b/30205>\
**Category:** Python Help\
**Created:** [July 24, 2023, 5:00pm UTC](https://discuss.python.org/t/has-sys-setrecursionlimit-behaviour-changed-in-python-3-12b/30205 "2023-07-24T17:00:31Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![lelit](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/lelit/32/13650_2.png) [@lelit](https://discuss.python.org/u/lelit)\
**Post date:** [July 24, 2023, 5:00pm UTC](https://discuss.python.org/t/has-sys-setrecursionlimit-behaviour-changed-in-python-3-12b/30205/1 "2023-07-24T17:00:31Z")

</div>

Hi all,  
today I tried to understand a test failure I’m seeing trying out [python-rapidjson](https://github.com/python-rapidjson/python-rapidjson) under Python 3.12b4.

One particular test (see tests/test\_circular.py#L45-L70 [link removed to honor the “new user limitation”…]) uses `sys.setrecursionlimit()` to assert that the underlying C++ implementation (that uses `Py_EnterRecursiveCall()`, see [for example](https://github.com/python-rapidjson/python-rapidjson/blob/master/rapidjson.cpp#L2565-L2570) properly raises a `RecursionError`.

Up to Python 3.11, it does work as expected, while on 3.12 it does not, or more precisely I do not seem able to control the recursion depth: it is like the recursion limit is _fixed_, and whatever value I pass to `sys.setrecursionlimit()` does not influence that.

I looked around to find news about changes related to either `sys.setrecursionlimit()` or `Py_EnterRecursiveCall()`, but found nothing. So I poked into the source of stdlib `json` module, and seeing it very similar to the `rapidjson` code, I tried to replicate the “problem” with that, and indeed I see a similar result.

Under Python 3.11 I see this:

```auto
$ python3.11
Python 3.11.4 (main, Jun 7 2023, 10:13:09) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> d = {}
>>> for x in range(10_000):
... d = {'k': d}
... 
>>> import json
>>> foo = json.dumps(d)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.11/json/ __init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
RecursionError: maximum recursion depth exceeded while encoding a JSON object
>>> import sys
>>> sys.setrecursionlimit(100_000)
>>> foo = json.dumps(d)
>>> 

```

With Python 3.12b4 I get this instead:

```auto
$ python3.12
Python 3.12.0b4 (main, Jul 13 2023, 14:24:02) [GCC 13.1.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> d = {}
>>> for x in range(10_000):
... d = {'k': d}
... 
>>> import json
>>> foo = json.dumps(d)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.12/json/ __init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
RecursionError: maximum recursion depth exceeded while encoding a JSON object
>>> import sys
>>> sys.setrecursionlimit(100_000)
>>> foo = json.dumps(d)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.12/json/ __init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
RecursionError: maximum recursion depth exceeded while encoding a JSON object
>>> sys.setrecursionlimit(10_000_000)
>>> foo = json.dumps(d)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.12/json/ __init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
RecursionError: maximum recursion depth exceeded while encoding a JSON object
>>> 

```

Am I missing something, or effectively the recursion constraint has been changed in some way?

Thanks in advance for any clarification.

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<div class="post-metadata">

**Author:** ![hauntsaninja](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/hauntsaninja/32/12451_2.png) [@hauntsaninja](https://discuss.python.org/u/hauntsaninja)\
**Post date:** [July 25, 2023, 6:59pm UTC](https://discuss.python.org/t/has-sys-setrecursionlimit-behaviour-changed-in-python-3-12b/30205/2 "2023-07-25T18:59:41Z")

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Thanks for testing with the betas! I think this is worth opening an issue on the CPython repo for, would you mind doing so? Possibly related to [GH-91079: Decouple C stack overflow checks from Python recursion checks. by markshannon · Pull Request #96510 · python/cpython · GitHub](https://github.com/python/cpython/pull/96510)

Edit: confirmed it bisects to that PR, opened an issue here: [Regression in 3.12 beta in json.dump deeply nested dict · Issue #107263 · python/cpython · GitHub](https://github.com/python/cpython/issues/107263)

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<div class="post-metadata">

**Author:** ![lelit](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/lelit/32/13650_2.png) [@lelit](https://discuss.python.org/u/lelit)\
**Post date:** [July 25, 2023, 7:41pm UTC](https://discuss.python.org/t/has-sys-setrecursionlimit-behaviour-changed-in-python-3-12b/30205/3 "2023-07-25T19:41:07Z")

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Thanks so much!