How to force Plotly to use a certain port when rendering in a browser?

Question

Before somebody marks this question as a duplicate, I should mention that I'm not using Plotly Dash or a Jupyter Notebook which were what all of the other SO answers I could find were pertaining to.

Using regular Plotly and a regular Python script from a terminal, in Ubuntu 20.04, when I run a script, for example this:

import numpy as np
import plotly.graph_objects as PlotlyGraphObjects

SHOW_PLOTLY_MOUSEOVERS = False

def main():

    lidar_points = np.array([[1, 2, 3],
                             [4, 5, 6],
                             [7, 8, 9]], dtype=np.float32)

    print('\n' + 'lidar_points.shape')
    print(lidar_points.shape)

    s3dPoints = PlotlyGraphObjects.Scatter3d(x=lidar_points[0], y=lidar_points[1], z=lidar_points[2], mode='markers', marker={'size': 1})

    plotlyFig = PlotlyGraphObjects.Figure(data=[s3dPoints])
    plotlyFig.update_layout(scene_aspectmode='data')

    if not SHOW_PLOTLY_MOUSEOVERS:
        plotlyFig.update_layout(hovermode=False)
        plotlyFig.update_layout(scene=dict(xaxis_showspikes=False,
                                           yaxis_showspikes=False,
                                           zaxis_showspikes=False))
    # end if

    plotlyFig.show()


# end function
if __name__ == '__main__':
    main()

Plotly opens a new tab in Chrome (my default browser) and shows the data:

In this particular example Plotly choose port 43001, presumably because it determined that port was available. Is there a way I can set which port Plotly uses, or at least force it to use the same port each time?

The reason I'm asking is I have to use Plotly code inside a Docker container and if I can force Plotly to use a certain port then I can open that port to the host when starting the container, but since I don't currently know how to force Plotly to use a certain port I'm unable to see the rendering. I checked the documentation for Plotly show https://plotly.com/python/renderers/ and surprisingly did not find anything pertaining to setting the port.

Answer 1

Delving into the plotly codes, I found that the server's port is set to '0', which is going to be translated to a random available number.

https://github.com/plotly/plotly.py/blob/2b6ec1e16bebe260dfc673db869805f7ceb86e00/packages/python/plotly/plotly/io/_base_renderers.py#L705

As the '0' is hard coded, you need to overwrite the entire function that opens browser. Run this script, e.g., in a start-up script.

import webbrowser

import plotly
from plotly.io._base_renderers import BaseHTTPRequestHandler, HTTPServer


def open_html_in_browser(html, using=None, new=0, autoraise=True):
    """
    Display html in a web browser without creating a temp file.
    Instantiates a trivial http server and uses the webbrowser module to
    open a URL to retrieve html from that server.
    Parameters
    ----------
    html: str
        HTML string to display
    using, new, autoraise:
        See docstrings in webbrowser.get and webbrowser.open
    """
    if isinstance(html, str):
        html = html.encode("utf8")

    browser = None

    if using is None:
        browser = webbrowser.get(None)
    else:
        if not isinstance(using, tuple):
            using = (using,)
        for browser_key in using:
            try:
                browser = webbrowser.get(browser_key)
                if browser is not None:
                    break
            except webbrowser.Error:
                pass

        if browser is None:
            raise ValueError("Can't locate a browser with key in " + str(using))

    class OneShotRequestHandler(BaseHTTPRequestHandler):
        def do_GET(self):
            self.send_response(200)
            self.send_header("Content-type", "text/html")
            self.end_headers()

            bufferSize = 1024 * 1024
            for i in range(0, len(html), bufferSize):
                self.wfile.write(html[i : i + bufferSize])

        def log_message(self, format, *args):
            # Silence stderr logging
            pass

    server = HTTPServer(("127.0.0.1", 54321), OneShotRequestHandler)  # fixed port number
    browser.open(
        "http://127.0.0.1:%s" % server.server_port, new=new, autoraise=autoraise
    )

    server.handle_request()


# overwrite the original implementation
plotly.io._base_renderers.open_html_in_browser = open_html_in_browser