Archived discussions · Captured October 28, 2026

controlling format of axis labels for datetime axis

Jonathan_SlavinApr 10, 2017 #1

Hi,

I’ve been plotting data where the x values are datetime objects. Using the x_axis_type = ‘datetime’ argument to figure, that axis is labeled correctly but with a very short format: hh:mm (where hh is the hour and mm is the minutes). I’d like to have a longer string used for the date which would include the month and day, even though it is redundant (i.e. every point will have the same month and day in most cases). How do I do that? I was looking at the methods and attributes of the axis and nothing jumped out at me.

Thanks,

Jon

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BryanApr 11, 2017 #2

Hi,

When you specify "datetime" then your axis gets configured with a DatetimeTickFormatter, which can be accessed by, e.g.

plot.xaxis.formatter

The different scales for DatetimeTickFormatter can be configured at a fine level:

formatters — Bokeh 3.3.2 Documentation

However, I notice that there is nothing about this in the users guide. It would be good to add something about this there as well. I'd encourage you to open a GitHub issue for this (and also submit a PR if you are able).

Thanks,

Bryan

···

On Apr 10, 2017, at 13:35, Jonathan Slavin <jslavin@cfa.harvard.edu> wrote:

Hi,

I've been plotting data where the x values are datetime objects. Using the x_axis_type = 'datetime' argument to figure, that axis is labeled correctly but with a very short format: hh:mm (where hh is the hour and mm is the minutes). I'd like to have a longer string used for the date which would include the month and day, even though it is redundant (i.e. every point will have the same month and day in most cases). How do I do that? I was looking at the methods and attributes of the axis and nothing jumped out at me.

Thanks,
Jon

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Jonathan_SlavinApr 11, 2017 #3

Hi Bryan,

Thanks for your response. I was looking at that page and having a hard time figuring out what was going wrong with my attempts to set the values of some attributes. I discovered that I had an older version of bokeh installed and the class definition of the DatetimeTickFormatter has changed substantially. After updating, I can now set the attributes (.e.g hourmin) as I wanted.

This has led me to another issue, however. In maplotlib the datetime tick labels that are too long can be made to angle diagonally so that they don’t overlap. Can that be done with bokeh?

Regards,

Jon

···

On Tue, Apr 11, 2017 at 12:43 PM, Bryan Van de ven bryanv@continuum.io wrote:

For more options, visit https://groups.google.com/a/continuum.io/d/optout.

Hi,

When you specify “datetime” then your axis gets configured with a DatetimeTickFormatter, which can be accessed by, e.g.
    plot.xaxis.formatter
The different scales for DatetimeTickFormatter can be configured at a fine level:
    [http://bokeh.pydata.org/en/latest/docs/reference/models/formatters.html#bokeh.models.formatters.DatetimeTickFormatter](http://bokeh.pydata.org/en/latest/docs/reference/models/formatters.html#bokeh.models.formatters.DatetimeTickFormatter)
However, I notice that there is nothing about this in the users guide. It would be good to add something about this there as well. I’d encourage you to open a GitHub issue for this (and also submit a PR if you are able).

Thanks,

Bryan

On Apr 10, 2017, at 13:35, Jonathan Slavin jslavin@cfa.harvard.edu wrote:

Hi,

I’ve been plotting data where the x values are datetime objects. Using the x_axis_type = ‘datetime’ argument to figure, that axis is labeled correctly but with a very short format: hh:mm (where hh is the hour and mm is the minutes). I’d like to have a longer string used for the date which would include the month and day, even though it is redundant (i.e. every point will have the same month and day in most cases). How do I do that? I was looking at the methods and attributes of the axis and nothing jumped out at me.

Thanks,

Jon

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Jonathan D. Slavin Harvard-Smithsonian CfA
jslavin@cfa.harvard.edu 60 Garden Street, MS 83
phone: (617) 496-7981 Cambridge, MA 02138-1516
cell: (781) 363-0035 USA

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BryanApr 11, 2017 #4

Hi Bryan,

Thanks for your response. I was looking at that page and having a hard time figuring out what was going wrong with my attempts to set the values of some attributes. I discovered that I had an older version of bokeh installed and the class definition of the DatetimeTickFormatter has changed substantially. After updating, I can now set the attributes (.e.g hourmin) as I wanted.

Yes it's been changed for quite a white now. The old version was too easy to misconfigure in ways that caused hard to diagnose errors.

This has led me to another issue, however. In maplotlib the datetime tick labels that are too long can be made to angle diagonally so that they don't overlap. Can that be done with bokeh?

That's a property of the axis:

Appearance — Bokeh 3.3.2 Documentation

Thanks,

Bryan

···

On Apr 11, 2017, at 13:25, Slavin, Jonathan <jslavin@cfa.harvard.edu> wrote:

Regards,
Jon

On Tue, Apr 11, 2017 at 12:43 PM, Bryan Van de ven <bryan@bokeh.org> wrote:
Hi,

When you specify "datetime" then your axis gets configured with a DatetimeTickFormatter, which can be accessed by, e.g.

plot.xaxis.formatter

The different scales for DatetimeTickFormatter can be configured at a fine level:

formatters — Bokeh 3.3.2 Documentation

However, I notice that there is nothing about this in the users guide. It would be good to add something about this there as well. I'd encourage you to open a GitHub issue for this (and also submit a PR if you are able).

Thanks,

Bryan

> On Apr 10, 2017, at 13:35, Jonathan Slavin <jslavin@cfa.harvard.edu> wrote:
>
> Hi,
>
> I've been plotting data where the x values are datetime objects. Using the x_axis_type = 'datetime' argument to figure, that axis is labeled correctly but with a very short format: hh:mm (where hh is the hour and mm is the minutes). I'd like to have a longer string used for the date which would include the month and day, even though it is redundant (i.e. every point will have the same month and day in most cases). How do I do that? I was looking at the methods and attributes of the axis and nothing jumped out at me.
>
> Thanks,
> Jon
>
> --
> You received this message because you are subscribed to the Google Groups "Bokeh Discussion - Public" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to bokeh+unsubscribe@continuum.io.
> To post to this group, send email to bokeh@continuum.io.
> To view this discussion on the web visit https://groups.google.com/a/continuum.io/d/msgid/bokeh/bb7be028-787c-43de-8d03-a0ab4d02316c%40continuum.io\.
> For more options, visit https://groups.google.com/a/continuum.io/d/optout\.

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--
________________________________________________________
Jonathan D. Slavin Harvard-Smithsonian CfA
jslavin@cfa.harvard.edu 60 Garden Street, MS 83
phone: (617) 496-7981 Cambridge, MA 02138-1516
cell: (781) 363-0035 USA
________________________________________________________

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Jonathan_SlavinApr 11, 2017 #5

Thanks for the pointer to how to change label orientation. I should be all
set now.

···

On Tue, Apr 11, 2017 at 3:27 PM, Bryan Van de ven <bryan@bokeh.org> wrote:

> On Apr 11, 2017, at 13:25, Slavin, Jonathan <jslavin@cfa.harvard.edu> > wrote:
>
> Hi Bryan,
>
> Thanks for your response. I was looking at that page and having a hard
time figuring out what was going wrong with my attempts to set the values
of some attributes. I discovered that I had an older version of bokeh
installed and the class definition of the DatetimeTickFormatter has changed
substantially. After updating, I can now set the attributes (.e.g hourmin)
as I wanted.

Yes it's been changed for quite a white now. The old version was too easy
to misconfigure in ways that caused hard to diagnose errors.

> This has led me to another issue, however. In maplotlib the datetime
tick labels that are too long can be made to angle diagonally so that they
don't overlap. Can that be done with bokeh?

That's a property of the axis:

http://bokeh.pydata.org/en/latest/docs/user_guide/
styling.html#tick-label-orientation

Thanks,

Bryan

--
________________________________________________________
Jonathan D. Slavin Harvard-Smithsonian CfA
jslavin@cfa.harvard.edu 60 Garden Street, MS 83
phone: (617) 496-7981 Cambridge, MA 02138-1516
cell: (781) 363-0035 USA
________________________________________________________

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Chris_WithersJun 15, 2021 #6

From the docs: “By default, only the first format string passed for each time scale will be used” - what is the second format there for and how do I get it to be used? (the second item in all the default lists looks to be what I want!)

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BryanJun 15, 2021 #7

@Chris_Withers please prefer making new topics over necro-bumping four year old ones.

I don’t actually think additional formats are ever used. The datetime ticker formatters took inspiration from another plotting system we had worked on years prior that does use multiple formats per scale in some ways. But we never actually found any demand or use for it in Bokeh, and that functionalit was never really implemented beyond the property types. So AFAIK that comment in the docs is just some ancient, decade-old cruft that ought to be removed. An issue or pull request to do so would be appropriate. ^[1]

Edit: I have gone ahead and made an issue for the API change fix at 3.0 but if you want to contribute something for the docs change now/sooner that is certainly appreciated.

github.com/bokeh/bokeh

Simplify DatatimeTickFormatter format properties

opened 07:22PM - 15 Jun 21 UTC

bryevdv

type: task tag: component: bokehjs tag: API: models

Currently `DateTimetickFormatter` accepts a *list* of formats for each time scal…e. This is mostly just taken from the Chaco implentation that was used as a reference in very early days. But it's unclear what causes a given format to be chosen out of that list. The docs state "By default, only the first format string passed for each time scale will be used". Looking at the code, it seem like the formatter might try to sort the formats based on their length when applied to "now", and use the first of *that* list. Either way it is complicated and seems unnecessary and useless as is. I propose for 3.0 to change the property types to be single `String` instead of `List(String)`, but add an `accepts` to keep existing code that sets lists of 1-length strings working (with a warning). This would still be breaking if anyone is doing e.g. `formatter.minsec[0]` but I suspect that is very uncommon at best. cc @bokeh/dev

We really probably ought to also change the property types to just accept single strings for formats, instead of lists of strings, but that is a more involved undertaking. ↩︎

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Chris_WithersJun 17, 2021 #8

Thanks! I was tempted to do a fly-by PR to simplify the docs, but it sounds like there’s complexity in the implementation that means that may not be a good idea…

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BryanJun 17, 2021 #9

If you are inclined, for now a PR just to remove that comment would also be useful.

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systemJul 21, 2021 #10

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