How to use the colorcet.cm.keys function in colorcet

from bokeh.models import WMTSTileSource
url = 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{Z}/{Y}/{X}.jpg'
wmts = gv.WMTS(WMTSTileSource(url=url))

stream = hv.streams.Stream.define('HourSelect', hour=0)()
points = hv.Points(ddf, kdims=['dropoff_x', 'dropoff_y'])
dmap = hv.util.Dynamic(points, operation=lambda obj, hour: obj.select(dropoff_hour=hour).relabel('Hour of Day: %d' % hour),
                       streams=[stream])

# Apply aggregation
aggregated = aggregate(dmap, link_inputs=True, streams=[hv.streams.RangeXY], width=1200, height=600)

# Shade the data
class ColormapPicker(hv.streams.Stream):
    colormap   = param.ObjectSelector(default=cm["fire"],
                                      objects=[cm[k] for k in cm.keys() if not '_' in k])

cmap_picker = ColormapPicker(rename={'colormap': 'cmap'}, name='')
shaded = shade(aggregated, link_inputs=True, streams=[cmap_picker])

# Define PointerX stream, attach to points and declare DynamicMap for cross-section and VLine
pointer = hv.streams.PointerX(x=ddf.dropoff_x.loc[0].compute().iloc[0], source=points)
section = hv.util.Dynamic(aggregated, operation=lambda obj, x: obj.sample(dropoff_x=x),
                          streams=[pointer], link_inputs=False).relabel('')
vline = hv.DynamicMap(lambda x: hv.VLine(x), streams=[pointer])

# Define options
hv.opts("RGB [width=1200 height=600 xaxis=None yaxis=None fontsize={'title': '14pt'}] VLine (color='white' line_width=2)")
hv.opts("Curve [width=150 yaxis=None show_frame=False] (color='black') {+framewise} Layout [shared_axes=False]")

# Combine it all into a complex layout
hvobj = (wmts * shaded * vline) << section