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import holoviews as hv
from holoviews import opts
from holoviews import streams
hv.extension('bokeh')

The FreehandDraw stream adds a bokeh tool to the source plot, which allows freehand drawing on the plot canvas and makes the resulting paths available to Python. The tool supports the following actions:

Draw

Click and drag to draw a line or polygon, release mouse to stop drawing

Delete line

Tap a line to select it then press BACKSPACE key while the mouse is within the plot area.

The tool allows drawing lines and polygons by supplying it with a Path or Polygons object as a source. It also allows limiting the number of lines or polygons that can be drawn by setting num_objects to a finite number, causing the first line to be dropped when the limit is reached.



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path = hv.Path([])
freehand = streams.FreehandDraw(source=path, num_objects=3)

path.opts(
    opts.Path(active_tools=['freehand_draw'], height=400, line_width=10, width=400))

Whenever the data source is edited the data is synced with Python, both in the notebook and when deployed on the bokeh server. The data is made available as a dictionary of columns:



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freehand.data

Alternatively we can use the element property to get an Element containing the returned data:



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freehand.element