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UID:pretalx-pyconde-pydata-2026-88TTRY@pretalx.com
DTSTART;TZID=CET:20260414T114500
DTEND;TZID=CET:20260414T121500
DESCRIPTION:Python relies heavily on special values such as `None`\, `NotIm
 plemented`\, `Ellipsis`\, and `dataclasses.MISSING`. These values are not 
 incidental: they encode language semantics\, enable control flow between o
 bjects\, and shape API design.\n\nThis talk examines sentinel values as a 
 first-class concept in Python. We will look at why None is often the wrong
  representation for absence\, how NotImplemented enables double dispatch i
 n rich comparisons\, and where sentinel values appear throughout the stand
 ard library.\n\nA central focus is typing. While sentinel values are ubiqu
 itous at runtime\, Python currently has no standardized way to express the
 m precisely in type hints. We will examine why Optional\, overloads\, and 
 Literal fall short\, what limited narrowing is possible today\, and why cr
 eating a “real” custom sentinel with reliable type narrowing is still 
 unsolved.\n\nFinally\, we will discuss [PEP 661](https://peps.python.org/p
 ep-0661/)\, i.e.\, the deferred proposal to standardize sentinel values an
 d their typing semantics\, and what its deferral means in practice. Using 
 real-world examples\, including Pydantic’s experimental missing concept\
 , this talk provides a clear mental model for sentinel values and realisti
 c guidance for using them in typed Python codebases today.
DTSTAMP:20260412T141623Z
LOCATION:Merck Plenary (Spectrum)  [1st Floor]
SUMMARY:Sentinel Values in Python: Semantics\, Double Dispatch\, and the Li
 mits of Typing - Florian Wilhelm
URL:https://pretalx.com/pyconde-pydata-2026/talk/88TTRY/
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