Fix using .get_color() and friends in labels handling

[skirpichev]

PR Summary

This code was introduced in v2.1.1 and, apparently, wasn't tested, because .get_color() returns array.

Here is examples (raises ValueError):
sympy/sympy#13730 (comment)
or
https://travis-ci.org/diofant/diofant/jobs/316670834

PR Checklist

• Has Pytest style unit tests

[dstansby]

I don't think this works because (for example) string colors are valid, and 's'.any() doesn't make any sense - I've put an alternative fix in #10031, does that work for you?

[skirpichev]

I don't think this works

It does work for me (e.g. fix plotting tests in the Diofant), but apparently it breaks some matplotlib tests.

I've put an alternative fix in #10031, does that work for you?

Unfortunately, no. Now I see this exception:

=================================== FAILURES ===================================
____________________________ test_matplotlib_intro _____________________________

c = array([[ 0.12156863,  0.46666667,  0.70588235,  1.        ]]), alpha = None

    def to_rgba(c, alpha=None):
        """Convert `c` to an RGBA color.
    
        If `alpha` is not `None`, it forces the alpha value, except if `c` is
        "none" (case-insensitive), which always maps to `(0, 0, 0, 0)`.
        """
        # Special-case nth color syntax because it should not be cached.
        if _is_nth_color(c):
            from matplotlib import rcParams
            prop_cycler = rcParams['axes.prop_cycle']
            colors = prop_cycler.by_key().get('color', ['k'])
            c = colors[int(c[1]) % len(colors)]
        try:
>           rgba = _colors_full_map.cache[c, alpha]
E           TypeError: unhashable type: 'numpy.ndarray'

../../venv/dev/lib/python3.5/site-packages/matplotlib/colors.py:132: TypeError

During handling of the above exception, another exception occurred:

    @pytest.mark.skipif(matplotlib is None, reason="no matplotlib")
    def test_matplotlib_intro():
        """Examples from the 'introduction' notebook."""
        try:
            name = 'test'
            tmp_file = TmpFileManager.tmp_file
    
            p = plot(x)
            p = plot(x*sin(x), x*cos(x))
            p.extend(p)
            p[0].line_color = lambda a: a
            p[1].line_color = 'b'
            p.title = 'Big title'
            p.xlabel = 'the x axis'
            p[1].label = 'straight line'
            p.legend = True
            p.aspect_ratio = (1, 1)
            p.xlim = (-15, 20)
>           p.save(tmp_file('%s_basic_options_and_colors' % name))

diofant/plotting/tests/test_plot.py:80: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
diofant/plotting/plot.py:181: in save
    self._backend.save(path)
diofant/plotting/plot.py:966: in save
    self.process_series()
diofant/plotting/plot.py:945: in process_series
    if self.ax.legend():
../../venv/dev/lib/python3.5/site-packages/matplotlib/axes/_axes.py:497: in legend
    **kwargs)
../../venv/dev/lib/python3.5/site-packages/matplotlib/legend.py:1403: in _parse_legend_args
    handles, labels = _get_legend_handles_labels(axs, handlers)
../../venv/dev/lib/python3.5/site-packages/matplotlib/legend.py:1361: in _get_legend_handles_labels
    and not _in_handles(handle, label)):
../../venv/dev/lib/python3.5/site-packages/matplotlib/legend.py:1340: in _in_handles
    if (colors.to_rgba(f_h.get_color()) != colors.to_rgba(h.get_color())):
../../venv/dev/lib/python3.5/site-packages/matplotlib/colors.py:134: in to_rgba
    rgba = _to_rgba_no_colorcycle(c, alpha)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

c = array([[ 0.12156863,  0.46666667,  0.70588235,  1.        ]]), alpha = None

    def _to_rgba_no_colorcycle(c, alpha=None):
        """Convert `c` to an RGBA color, with no support for color-cycle syntax.
    
        If `alpha` is not `None`, it forces the alpha value, except if `c` is
        "none" (case-insensitive), which always maps to `(0, 0, 0, 0)`.
        """
        orig_c = c
        if isinstance(c, six.string_types):
            if c.lower() == "none":
                return (0., 0., 0., 0.)
            # Named color.
            try:
                # This may turn c into a non-string, so we check again below.
                c = _colors_full_map[c.lower()]
            except KeyError:
                pass
        if isinstance(c, six.string_types):
            # hex color with no alpha.
            match = re.match(r"\A#[a-fA-F0-9]{6}\Z", c)
            if match:
                return (tuple(int(n, 16) / 255
                              for n in [c[1:3], c[3:5], c[5:7]])
                        + (alpha if alpha is not None else 1.,))
            # hex color with alpha.
            match = re.match(r"\A#[a-fA-F0-9]{8}\Z", c)
            if match:
                color = [int(n, 16) / 255
                         for n in [c[1:3], c[3:5], c[5:7], c[7:9]]]
                if alpha is not None:
                    color[-1] = alpha
                return tuple(color)
            # string gray.
            try:
                return (float(c),) * 3 + (alpha if alpha is not None else 1.,)
            except ValueError:
                pass
            raise ValueError("Invalid RGBA argument: {!r}".format(orig_c))
        # tuple color.
        c = np.array(c)
        if not np.can_cast(c.dtype, float, "same_kind") or c.ndim != 1:
            # Test the dtype explicitly as `map(float, ...)`, `np.array(...,
            # float)` and `np.array(...).astype(float)` all convert "0.5" to 0.5.
            # Test dimensionality to reject single floats.
>           raise ValueError("Invalid RGBA argument: {!r}".format(orig_c))
E           ValueError: Invalid RGBA argument: array([[ 0.12156863,  0.46666667,  0.70588235,  1.        ]])

../../venv/dev/lib/python3.5/site-packages/matplotlib/colors.py:185: ValueError
=============== 1 failed, 4 passed, 2 xfailed in 133.04 seconds ================

(This test coming from https://github.com/diofant/diofant/blob/master/diofant/plotting/tests/test_plot.py).

[tacaswell]

@skirpichev Can you provide a minimal test that exercises the failing path?

[skirpichev]

@tacaswell, I'll try to do this.

[dstansby]

I've updated my PR so now it should hopefully work with arrays, give it another try @skirpichev

[jklymak]

It would be nice to see the use case that is breaking.

[skirpichev]

@jklymak, see this comment.

[jklymak]

I saw that comment. Sorry this broke something for you. What is the code that triggers the error?

[skirpichev]

@dstansby. yes - updated solution seems to be working.

[jklymak]

The root of the problem is that you are passing a 2-D array instead of a 1-D array as a color. @dstansby is fixing on our end #10031, but you could also fix on your end by making sure you only pass a 1-D array.

[tacaswell]

@skirpichev From how you are using plot in that test I assume that is not a plot from Matplotlib. Can you please provide an example using only Matplotlib functions / methods that reproduces your problem?

[jklymak]

I think the sympy folks are looking into it now.

[dstansby]

@jklymak I thought my PR superseeded this one?

[jklymak]

I was confused too. I think somehow the prs were linked and yours was committed on top of this one versus being separate.

[QuLogic]

Your commits follow this one; ergo merging it also means this is merged. There is no linkage except the commits.

[jklymak]

FWIW #10064 will wipe them both out ;-) Reviews welcome....