[Twisted-web] some questions about twisted.web

[glyph at divmod.com]

On 7 Apr, 07:47 pm, jack at chesspark.com wrote:
>>You can pass arbitrary command line options by writing a plugin.
>>=A0http://twistedmatrix.com/projects/core/documentation/howto/tap.html
>
>Which, as I recall, Glyph and others have discourged others from doing
>this.  Perhaps I am mistaken, but if twistd is intended for this
>purpose, why has this not become part of it all along?

Chris has already basically set the record straight here, but for future =

readers I just wanted to have a direct reply to this message and clear =

up a very unfortunate choice of acronyms.  Some of this is a summary of =

other things that have already been mentioned in this thread.

I definitely do not discourage the use of twistd for this purpose :). =

In fact I strongly recommend it.  Here's the history.

".tap" ("Twisted Application Pickle") files, and the associated "mktap" =

("make twisted application pickle") command-line utility, are strongly =

discouraged.  They've been deprecated for a long time, and they'll be =

gone soon.

"TAPs" ("Twisted Application *Plugins*") were originally plugins for =

"mktap".  That's why the naming is similar.  However, *they are now =

plugins for twistd*, and have been for some time.  Developers are =

strongly encouraged to use this interface, and to read the document =

linked above.

Before "TAPs" were plugins for twistd, the suggested configuration =

mechanism for twisted applications was to write a '.tac' file and tell =

your users to edit it.  Processing twistd's commandline arguments at =

this point was impossible without gratuitous hacks, so tac files were a =

better alternative.  However, as Jack noted, editing tac files is =

inconvenient, so we added the twistd plugin interface.  We now recommend =

that adding command-line arguments to your 'twistd' plugin is the way to =

go if you want run-time configuration for your twisted server =

application.

The technique that Chris suggested elsewhere in this thread, to set up =

correct command-line arguments for your plugin and then call twistd's =

run() function, is the currently supported way to invoke twistd's =

functionality from your own scripts.  This is what we use to support =

Divmod's "axiomatic" command, which is basically a database-configured =

version of "twistd".  A more expressive API for a wider variety of use- =

cases is forthcoming, but this technique should still work even once =

such an API has been added.

The document in question would really benefit from some updating; in =

particular, it would be good to move the mention of TAP files to some =

kind of endnote rather than being mentioned before the actual relevant =

features.