[Matplotlib-devel] Easier tick formatters

[Thomas Caswell]

It looks like something funny is going on with your branch (It looks like
there are some extra rebased commits), but other than that it look like a
good start.

Could you please open a PR so it can go through the normal code review
process / have CI run?

Tom

On Mon, Mar 9, 2020 at 10:45 AM Todd <toddrjen at gmail.com> wrote:

> 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?
>>
>
> Based on the input I have gotten so far, I have made a simplified version
> of the approach [1].  It only handles the cases for str and function (or
> rather callable, but I call it a function in the documentation).  These
> seem to handle most use-cases reasonably well.  As Antony pointed out, None
> is potentially confusing, and as Thomas pointed out IndexFormatter is
> deprecated.  That left only the empty NullFormatter (with an empty str),
> StrMethodFormatter (with any other str), and FuncFormatter (with a
> callable).
>
> Antony made a good case that we should keep the number of approaches as
> small as possible.  Since the NullFormatter is trivially handled with an
> empty str, and that is really what it is behind-the-scenes, that was an
> obvious one to cut.
>
> Antony made the good case that any str could be handled with str.format.
> I tried that approach initially, but the issue I ended up having is that,
> although it is obvious to experienced Python users, it isn't as obvious to
> newer users.  That would mean I would need to properly communicate this
> workaround to users in the documentation.  However, my attempts to do this
> ended up being longer, more complicated, and harder to understand than
> simply implementing the str case directly.  So I ended up keeping the str
> and function approaches.  Of course this decision is open to discussion.
>
> I also updated the documentation, tests, and examples to explain these new
> features.  Please take a look and let me know what you think.
>
> One open issue is that I did not change any examples currently using any
> of these formatters, I only added the new approach. I think it might be
> good to change some of the simpler examples of using formatters to use this
> new feature in order to make formatters seem more approachable, but I
> haven't done that yet.
>
> [1]
> https://github.com/toddrjen/matplotlib/commit/673e4b32bb8849d1de7f1180d5a48b13d68a6f34
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-- 
Thomas Caswell
tcaswell at gmail.com
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