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GeezerVison is showing github.com — DOC: Note AutoDateLocator date precision limits in units guide by vineoy · Pull Request #32566 · matplotlib/matplotlib

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@vineoy

@vineoy vineoy commented Nov 2, 2026 •
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PR summary

Following review feedback, the AutoDateLocator documentation now carries a short one-line note on the precision limits of matplotlib dates, linking to the explanation in the Plotting dates and strings explainer (galleries/users_explain/axes/axes_units.py), which is where the detailed discussion now lives. The original scope followed timhoffm's suggestion in #23493.

Because matplotlib dates are stored as floats of days since the epoch, nanosecond range timestamps lose their detail: close values collapse and the autoscaled view then spans years. I reproduced this locally and plotting the elapsed time as numpy.timedelta64 values gives a usable axis. The explainer section documents these limits and the options and links to the existing Date precision and epochs example.

Closes #23493

AI Disclosure

I used an AI coding assistant to explore the codebase and to run local experiments that verified the behavior documented here. I reviewed the docstring note and this PR text before submitting and the pre-commit checks pass locally on this branch.

PR quality check

  • Use an expressive title, e.g. "Fix title font property precedence"
  • [N/A] New and changed code is tested (docstring only, no code change)
  • [N/A] Plotting related features are demonstrated in an example
  • [N/A] New features and API changes have release notes
  • Documentation complies with general and docstring guidelines

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@vineoy
DOC: Note AutoDateLocator date precision limits
0ba867d
@github-actions github-actions Bot added the topic: date handling label Nov 2, 2026
@vineoy vineoy mentioned this pull request Nov 2, 2026
[Bug]: Plotting of Pandas DataFrame data with nanosecond timestamps #23493
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@github-actions github-actions Bot added the first-contribution label Nov 2, 2026
timhoffm
timhoffm reviewed Nov 3, 2026
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I'd rather have this explained in https://matplotlib.org/stable/users/explain/axes/axes_units.html

The note here should be shortend to something like

Date resolution is limited to approximately a microsecond. For details see [link].

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@vineoy
DOC: Move date precision details to axes units guide
e1c73ea 
Move the detailed explanation of Date resolution limits from the
AutoDateLocator docstring to the "Plotting dates and strings" explainer
page, and shorten the docstring note to a single sentence that links
there, as suggested in the review.
@github-actions github-actions Bot added the Documentation: user guide files in galleries/users_explain or doc/users label Nov 3, 2026
@vineoy vineoy changed the title DOC: Note AutoDateLocator date precision limits DOC: Note AutoDateLocator date precision limits in units guide Nov 3, 2026
@vineoy

vineoy commented Nov 3, 2026 •
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Done in e1c73ea - the AutoDateLocator note is now the shortened one-liner linking to the guide and the detailed explanation (including the nanosecond-timestamp example and the timedelta64 / set_epoch options) moved to the Date conversion section of the "Plotting dates and strings" explainer (galleries/users_explain/axes/axes_units.py).
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[Bug]: Plotting of Pandas DataFrame data with nanosecond timestamps

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@vineoy @timhoffm
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