---
hide-toc: true
myst:
  html_meta:
    description: >-
      Why repeated and skipped local times pass silently in the standard library:
      fold defaults to 0, there is no way to raise, and the parameter is hard to
      discover.
---

# Ambiguity is resolved without a word

When time zone offsets change—most commonly due to daylight saving time—a local
clock time may occur **twice** or **not at all**.

Python resolves these ambiguities with the `fold` parameter, which defaults to `0`.
That's not inherently wrong: having a deterministic default {ref}`is often useful <ambiguity-default>`.

The problem is that it’s difficult to handle ambiguity *explicitly*:

* There is no option to raise an error (instead of picking a default)
* The `fold` parameter is subtle and poorly discoverable
* Many users are unaware ambiguity exists at all

```python
# does `fold` matter here? Hard to tell!
datetime(2024, 10, 27, 2, 30, tzinfo=ZoneInfo("Europe/Amsterdam"), fold=1)
```

Without careful handling, code may interpret a repeated local time
differently than intended.

## How `whenever` solves this

`whenever` applies the same default as Python, but with an
`ImplicitDisambiguationWarning`; state `disambiguation=` to make the choice explicit:

```python
>>> dt = ZonedDateTime(2024, 10, 27, 2, 30, tz="Europe/Amsterdam", disambiguation="raise")
Traceback (most recent call last):
  ...
RepeatedTime: 2024-10-27 02:30:00 is repeated in time zone 'Europe/Amsterdam'
```