rebase patch for VPYTHON_HTTP_PORT and VPYTHON_NO_LAUNCH_BROWSER

[danx0r]

This partially addresses #217, by (optionally) not launching a browser and restricting the http port to a specified port.

This allows development with an open browser on a certain port, rather than having your default browser relaunched every time you run the code.

The relevant behavior is specified by two environment vars:

VPYTHON_HTTP_PORT

and

VPYTHON_NO_LAUNCH_BROWSER

[BruceSherwood]

I'm delighted with your enabling of a fixed port; the changing port number was simply a mistake on my part a long time ago and should have been fixed long ago. I suggest that we simply choose a port number, and I suggest 4200 (since "42" is the answer to everything...). I note that when using spyder a rerun really does use the existing browser page, though when using idle a rerun deletes the browser page (and the browser if only one page was open), just as with the present VPython. On the other hand, I don't understand (but am not necessarily opposed to) the need for being able to suppress the browser. It is already the case that when running in no-notebook mode no browser is invoked if there are no graphics statements in the program.

[danx0r]

Hi -- thanks for reviewing my pull request.

I'm running Ubuntu, and I have multiple workspaces that I can switch between. I typically run scripts from a terminal. Whenever vpython is invoked, it creates a new browser, often in the wrong workspace and with seemingly random size and screen position -- so letting the developer set up a single browser instance in their desired location and workspace, such that they just need to refresh it occasionally rather than hunt for a new browser window is very convenient.

In the larger picture, as outlined in #217 I would love to be able to build a website around vpython using the server built into vpython7 no_browser mode, but as presently architected that appears impossible because the server itself shuts down after each run. It seems to me the components are there to run a vpython program as a REST server that responds to multiple client sessions, but the way forward on that is not clear to me yet.

[BruceSherwood]

From your reply, I'm not sure what your opinion is on the two issues I raised. 1) Shall we eliminate VPYTHON_HTTP_PORT and just use one port number (4200)? 2) Why is there a need for VPYTHON_NO_LAUNCH_BROWSER, given that no browser is started if the program does not use graphics statements?

[danx0r]

I'm OK with default port=4200 but I would recommend allowing my suggested environment variable to override it in case of conflicts with other applications.

The reason to include VPYTHON_NO_LAUNCH_BROWSER is to enable a workflow where a browser is open and configured for testing and debugging, and does not get closed and re-opened on every test run. This may not be a problem if you always develop in an IDE such as Spyder, but if you use a stand-alone code editor and run the application from the command line it is very inconvenient to have the browser constantly close and reopen.

[BruceSherwood]

Thanks for explaining VPYTHON_NO_LAUNCH_BROWSER but I would have thought that it was unnecessary. Just open a browser to some random page, and put the browser where you want it to be, with a size you want, and you'll achieve the same result, won't you?

[danx0r]

Another reason to support the no-launch feature: as things work now, I am forced to use my default browser. I have both Firefox and Chrome installed, and there are good reasons to use one vs the other.

In any case, I think there is a larger issue here. My eventual goal is to build 3D applications that run on people's browsers but communicate with a server to provide the authoritative model of the system. VPython is tantalizingly close to being able to do that, but its habit of running a server and browser client for a single session and then quitting both makes this impossible.

I would encourage the VPython team to consider adding a mode of operation that would work more like Jupyter does, where a long-lived server listens on an HTTP port and clients can visit that URI:port from whatever browser or client they desire. I think this would open up a broader base of users and applications.

[danx0r]

One more use case: I may want to run vpython on a server in the cloud, and view the result on my local machine. These severs are headless, so an attempt to open a browser will probably cause an exception.

[mwcraig]

@danx0r -- we'd like to go ahead with this and also set a fixed default port (leaning towards 4200). You could add that change to this pull request or we can do it in a separate PR.

Either way can you please add your name to this file: https://github.com/vpython/vpython-jupyter/blob/master/CONTRIBUTORS.md

I'm not sure how much effort the new mode would be, but this hopefully addresses the immediate issues.

[mwcraig]

I'm going to go ahead and merge this -- PR #220 adds @danx0r as a contributor.

[danx0r]

Note that an old open PR #111 appears to cover the same ground and can probably be closed (not applied)