matplotlib-devel Mailing List for matplotlib

Darren Dale wrote:
> On Sunday 21 May 2006 15:26, John Hunter wrote:
> 
>>>>>>>"Eric" == Eric Firing <ef...@ha...> writes:
>>
>>    Eric> Suggestion: we say, "A color can be specified as a string in
>>    Eric> any of the following formats: standard color abbreviations,
>>    Eric> html names, hex, or a floating point number between 0 and 1.
>>    Eric> Or it can be given as a sequence of three numbers specifying
>>    Eric> R,G,B on a scale from 0 to 1."  Perfectly consistent and
>>    Eric> understandable, and clear in the code: "if
>>    Eric> is_string_like(c): convert it, else: pass it on as RGB.
>>    Eric> This consistency then makes it easy to distinguish between,
>>    Eric> and transparently handle, the case of a single color versus
>>    Eric> a sequence of colors.
>>
>>OK, you sold me.  I hadn't thought it through to see it was either a
>>string, RGB/A.  I like the simplicity of this.  So I'm +1 for your
>>suggestion with a deprecation period where we check for a scalar
> 
> 
> For what its worth, I'll also drop my objection.

Thanks. I will proceed.

Eric

On Sunday 21 May 2006 15:26, John Hunter wrote:
> >>>>> "Eric" == Eric Firing <ef...@ha...> writes:
>
>     Eric> Suggestion: we say, "A color can be specified as a string in
>     Eric> any of the following formats: standard color abbreviations,
>     Eric> html names, hex, or a floating point number between 0 and 1.
>     Eric> Or it can be given as a sequence of three numbers specifying
>     Eric> R,G,B on a scale from 0 to 1."  Perfectly consistent and
>     Eric> understandable, and clear in the code: "if
>     Eric> is_string_like(c): convert it, else: pass it on as RGB.
>     Eric> This consistency then makes it easy to distinguish between,
>     Eric> and transparently handle, the case of a single color versus
>     Eric> a sequence of colors.
>
> OK, you sold me.  I hadn't thought it through to see it was either a
> string, RGB/A.  I like the simplicity of this.  So I'm +1 for your
> suggestion with a deprecation period where we check for a scalar

For what its worth, I'll also drop my objection.

Darren

>>>>> "Eric" == Eric Firing <ef...@ha...> writes:

    Eric> Suggestion: we say, "A color can be specified as a string in
    Eric> any of the following formats: standard color abbreviations,
    Eric> html names, hex, or a floating point number between 0 and 1.
    Eric> Or it can be given as a sequence of three numbers specifying
    Eric> R,G,B on a scale from 0 to 1."  Perfectly consistent and
    Eric> understandable, and clear in the code: "if
    Eric> is_string_like(c): convert it, else: pass it on as RGB.
    Eric> This consistency then makes it easy to distinguish between,
    Eric> and transparently handle, the case of a single color versus
    Eric> a sequence of colors.

OK, you sold me.  I hadn't thought it through to see it was either a
string, RGB/A.  I like the simplicity of this.  So I'm +1 for your
suggestion with a deprecation period where we check for a scalar

I just looked in cbook and we did indeed have an is_scalar function
but it looked broken so I replaced it with

def is_scalar(obj):
    try: obj+1
    except TypeError: return False
    else: return True


As for looks_like_color, I never use it (in fact was not aware of it
til you mentioned it).  I think a function "is_colorlike" is a
potentially useful function, but as you say it is best implemented
with duck typing, something like

def is_colorlike(x):
    try: colorConverter.to_rgba(x)
    except: return False
    else: return True

JDH
  

John Hunter wrote:
>>>>>>"Eric" == Eric Firing <ef...@ha...> writes:
> 
> 
>     Eric> John, I think all the ambiguity that you mention below comes
>     Eric> from one source: the use of a single float to indicate a
>     Eric> greyscale.  Do we really need this? It is not supported by
>     Eric> colors.looks_like_color().  It could be replaced by a string
>     Eric> representation of the float (e.g., '0.75') or by a more
>     Eric> specific string, such as 'g0.75' or 'grey0.75'.  I think
>     Eric> this would be a big net gain for mpl.  We lose a lot of
>     Eric> flexibility, convenience, and consistency by allowing the
>     Eric> float-is-grey form.
> 
> this is a bug in looks_like_color -- ColorConverter, for example,
> supports it.

I suspect that all support of this form does occur via ColorConverter; 
it is interesting that the looks_like_color bug has not caused 
objections.  looks_like_color is used in only two places: Axes.quiver, 
which therefore does not support the present float-as-grayscale form, 
and Collection._get_color.  The consequence is that the collection rc 
settings also do not support float-as-grayscale, but nobody has noticed, 
or if they have, they have not been greatly bothered.

I also suspect that we should not have looks_like_color at all--it 
probably makes more sense to simply try to convert the object, and catch 
an exception if it is not convertable.  If the object does look like a 
color, then chances are one wants to convert it anyway, so why go 
through most of the logic twice.  (For compatibility, looks_like_color 
could simply do this--try to convert, return True on success and False 
on failure.)

> 
> What flexibility do we lose by supporting grayscale as float? As long
> as we have a policy of how we resolve ambiguity, I think we're OK.

Maybe OK, but not good. It is much better to avoid ambiguity entirely 
than to have to implement and explain an ambiguity resolution policy, 
when avoiding the ambiguity entails no loss in flexibility.

Present situation: we have to say something like, "(0.3, 0.4, 0.2) is a 
single RGB, but (0.3, 0.4) is a pair of greyscales".  That's ugly and 
inconsistent, both from the users' standpoint and in terms of what it 
requires in the code.

Suggestion: we say, "A color can be specified as a string in any of the 
following formats: standard color abbreviations, html names, hex, or a 
floating point number between 0 and 1.  Or it can be given as a sequence 
of three numbers specifying R,G,B on a scale from 0 to 1."  Perfectly 
consistent and understandable, and clear in the code: "if 
is_string_like(c): convert it, else: pass it on as RGB.  This 
consistency then makes it easy to distinguish between, and transparently 
handle, the case of a single color versus a sequence of colors.

(I posed everything in terms of RGB rather than RGBA, but the idea is 
the same.)

> Eg, ef we have a four-tuple of floats in a case where it could mean
> four grays or one RGB, we can choose to resolve it one way or the
> other.  I think this is a corner case and wouldn't come up to often.

But when it does come up, sometimes the disambiguation will not do what 
the user expected.  It is a fundamentally bad design, and it will bite 
people as long as it stays in place.

> As long as we have a way of disambiguating, eg adopting your 'g0.75'
> or 0.75' as a valid string, we retain flexibility and compatibility.

My proposal retains flexibility and increases simplicity and consistency 
by sacrificing the compatibility.  I think this is a case where it is 
worth it to do so.

> 
> I also use the float-as-grayscale not too infrequently....

But maybe with a long deprecation period, you wouldn't terribly mind 
occasionally changing (0.2, 0.3) to ('0.2', '0.3')?  (I know, it is easy 
for me because I am not the one who has to deal with it.)

Eric

>>>>> "Darren" == Darren Dale <dd...@co...> writes:

    Darren> slightly off-topic: Will mpl ever go 1.0? That's not meant
    Darren> to be flippant. I thought their was some pride in being
    Darren> beta.

I figured we would go to 1.0 when we run out of 0.88, 0.89, 0.90....

I think the API is pretty stable already, and suspect we won't be able
to guarantee much more stability after 1.0.  Think about pygtk -- it
changed like a madman from 1.6 to 1.99 to 2.2 to 2.4...  Sure, Numeric
was pretty stable after 10 years and 23 major releases, but then that
was broken with numarray and numpy.  I'm not sure that API stability
above and beyond what we are already providing exists that much in the
wild, so 1.0 is probably more of a psychological landmark than
anything else.  But maybe I'm just crazy.

I would like to fix the axis handling to be more flexible (eg, multiple
y axis lines per plot, detacable axis lines, etc) before 1.0.  

JDH

>>>>> "Eric" == Eric Firing <ef...@ha...> writes:

    Eric> John, I think all the ambiguity that you mention below comes
    Eric> from one source: the use of a single float to indicate a
    Eric> greyscale.  Do we really need this? It is not supported by
    Eric> colors.looks_like_color().  It could be replaced by a string
    Eric> representation of the float (e.g., '0.75') or by a more
    Eric> specific string, such as 'g0.75' or 'grey0.75'.  I think
    Eric> this would be a big net gain for mpl.  We lose a lot of
    Eric> flexibility, convenience, and consistency by allowing the
    Eric> float-is-grey form.

this is a bug in looks_like_color -- ColorConverter, for example,
supports it.

What flexibility do we lose by supporting grayscale as float? As long
as we have a policy of how we resolve ambiguity, I think we're OK.
Eg, ef we have a four-tuple of floats in a case where it could mean
four grays or one RGB, we can choose to resolve it one way or the
other.  I think this is a corner case and wouldn't come up to often.
As long as we have a way of disambiguating, eg adopting your 'g0.75'
or 0.75' as a valid string, we retain flexibility and compatibility.

I also use the float-as-grayscale not too infrequently....

JDH