[Matplotlib-devel] Easier tick formatters

[Thomas Caswell]

Interesting, I am weakly in favor of this.

I am normally very hesitant about adopting heuristics, but these seem well
defined.  If we do this, we should drop the last rule as IndexFormatter is
scheduled to be deprecated in in 3.3 and is a bit problematic in other ways.

I don't see any back-compatibility concerns (as none of those inputs work
now).

Tom

On Wed, Mar 4, 2020 at 10:03 PM Todd <toddrjen at gmail.com> wrote:

> Currently setting up the tick formatting on matplotlib requires you to
> import a formatter from the ticker module, create an instance of that
> formatter, then pass that to the axis.  This makes sense for complicated
> formatting.  However, there are some obvious cases where we can probably
> infer the type of formatting someone wants to do if we are just given the
> formatter content.  For example
>
>    * '' is probably going to be the null formatter
>    * A callable, besides a formatter instance, is probably going to be a
> function formatter
>    * A sequence or numpy array is probably going to be an index or fixed
> formatter, depending on the locator
>    * Any other string is probably going to be a format string formatter or
> string method formatter.
>
> So I think we could allow the `set_major_formatter` and `set_minor_formatter`
> to take certain sorts of inputs and create the formatter automatically for
> the user, making such cases much, much easier.  Specifically, I propose the
> following inputs be accepted:
>
>    * `None` sets it to the default formatter
>    * A callable (besides a formatter instance) is set to be a FuncFormatter
>    * An empty string, `''`, is set to be a NullFormatter
>    * Any other string is a StrMethodFormatter
>    * An abc.collections.Sequence subclass or numpy ndarray subclass is an
> IndexFormatter, unless the axis is using a FixedLocator in which case it is
> a FixedLocator.  We could restrict this to just lists and numpy arrays only.
>
> Any thoughts?
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-- 
Thomas Caswell
tcaswell at gmail.com
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