# PEP 661: Sentinel Values

**URL:** <https://discuss.python.org/t/pep-661-sentinel-values/9126>\
**Category:** PEPs\
**Created:** [June 6, 2021, 8:07am UTC](https://discuss.python.org/t/pep-661-sentinel-values/9126 "2021-06-06T08:07:06Z")\
**Posts on this page:** 1\
**Showing post:** 345

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**Author:** ![tmk](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/tmk/32/10935_2.png) [@tmk](https://discuss.python.org/u/tmk)\
**Post date:** [April 30, 2026, 11:25am UTC](https://discuss.python.org/t/pep-661-sentinel-values/9126/345 "2026-04-30T11:25:26Z")

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Sorry, another thought I had:

Is it somehow possible to make sentinels work with `match` by, e.g., supporting something like the following?

```python
MISSING = sentinel("MISSING")

def next_value(default: int | MISSING = MISSING):
  match default:
    case MISSING(): # note the parentheses here to avoid a catch-all match
      print("missing value")
    case val: # this is now `int`
      ...

```

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