feat: Expose NoUpdate type

[ytausch]

Closes #2800.

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • expose dash.NoUpdate
• I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR -> not needed

optionals

• I have added entry in the CHANGELOG.md
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • this GitHub #PR number updates the dash docs
  • here is the show and tell thread in Plotly Dash community

[T4rk1n]

Maybe we should add obj is NoUpdate or ... in the conditions of NoUpdate.is_no_update if this is exposed so it could be used as is.

[ytausch]

Isn't this already the case? If you mean an isinstance check.

dash/dash/_no_update.py

Lines 1 to 9 in 1f4337a

	class NoUpdate:
	def to_plotly_json(self): # pylint: disable=no-self-use
	return {"_dash_no_update": "_dash_no_update"}
	@staticmethod
	def is_no_update(obj):
	return isinstance(obj, NoUpdate) or (
	isinstance(obj, dict) and obj == {"_dash_no_update": "_dash_no_update"}
	)

[ytausch]

Ah, you referred back to the original issue. I added the condition.

[T4rk1n]

Looks good, just a formatting issue.

[T4rk1n]

💃 Thank you.