如何在HoloViews中为点图手动设置颜色栏的刻度位置？

Question

我有以下代码：

import numpy as np
import holoviews as hv
from bokeh.models import FixedTicker
hv.extension('bokeh')

points = hv.Points(np.random.randint(-3, 4, (20, 3)), vdims=['interval'])
points.opts(
    color='interval',
    size=10, 
    colorbar=True,
    color_levels=7,
    colorbar_opts={
        'major_label_overrides': {
            -3: 'high', 
            -2: 'medium', 
            -1: 'low',
            0: 'none', 
            1: 'low', 
            2: 'medium', 
            3: 'high'
        },
        'major_label_text_align': 'left',
    },
    cmap='RdYlGn',
)

哪个会产生类似的内容：

但是，我想更改刻度位置（到颜色容器的中间）。但是，当我将以下项目添加到colorbar_opts字典中时：

'ticker': FixedTicker(ticks=[-3, -2, -1, 0, 1, 2, 3]),

我收到此错误：

Traceback (most recent call last):

  File "C:\Users\pablo\AppData\Local\Continuum\anaconda3\envs\sandbox-py3.7\lib\site-packages\holoviews\plotting\bokeh\element.py", line 1017, in _init_glyphs
    renderer, glyph = self._init_glyph(plot, mapping, properties)

  File "C:\Users\pablo\AppData\Local\Continuum\anaconda3\envs\sandbox-py3.7\lib\site-packages\holoviews\plotting\bokeh\element.py", line 1561, in _init_glyph
    self._draw_colorbar(plot, v, k[:-12])

  File "C:\Users\pablo\AppData\Local\Continuum\anaconda3\envs\sandbox-py3.7\lib\site-packages\holoviews\plotting\bokeh\element.py", line 1392, in _draw_colorbar
    **dict(opts, **self.colorbar_opts))

TypeError: MetaModel object got multiple values for keyword argument 'ticker'

如何在颜色栏中设置刻度线的位置？

我正在使用Python 3.7，HoloViews 1.11.2和Bokeh 1.0.4