[Tutor] Threads.... More Despair....

[Allan Crooks]

This'll be my first piece of help I've ever given anyone on this list! I'm doing my bit! :)

<snip>

> ## Function write() writes a list to the database
> def write(inputtage):
> 	time=inputtage[0]
> 	data_string=inputtage[1]
> 	db.Execute("insert into data values(%f, '%s')" %(time, data_string))
> 	return 'ok'
> 
> tik_tok=time.time()
> surprize=random.choice(['Hellbilly', 'Crunchy Tack', 'Feeble'])
> the_madness=(tik_tok, surprize)
> thread.start_new_thread(write(the_madness))
> 
> gets this error:
> 
> Traceback (most recent call last):
>   File "dbwrite.py", line 21, in ?
>     thread.start_new_thread(write(the_madness))
> TypeError: start_new_thread requires at least 2 arguments; 1 given
> 
> Fair enough. I looked again at my spanking new copy of "Python Standard 
> Library" and noticed that in the example 'start_new_thread(worker, ())'. In 
> the example, worker() does not accept an argument. Hrm.
> 
> In the spirit of blind flailing I attempted:
> 
> thread.start_new_thread(write(the_madness),())
> 
> and got:
> 
> Traceback (most recent call last):
>   File "dbwrite.py", line 21, in ?
>     thread.start_new_thread(write(the_madness), ())
> TypeError: first arg must be callable
> 
> for my troubles. Since I don't have a clue what is going on this was not a 
> big surprize! :-)

The problem is the slight misunderstanding of what happens when you put:

thread.start_new_thread(write(the_madness),())

What you mean to say is:

thread.start_new_thread(write, (the_madness,)).

The whole point of creating a new thread is to invoke some function. The function may, or may not need arguments.

To create a new thread, you need to supply the function you want to run, and any supplementary arguments.

The function is obviously "write", and the only argument you are supplying is "the_madness". But when you put write(the_madness), the function is actually being executed, and then returns a value (looking at the code, it's the string 'ok'). So:

thread.start_new_thread(write(the_madness),())

is evaluated to:

thread.start_new_thread('ok', ())

and then the thread module complains because it is unable to run the function 'ok' (which is a string, not a function of any sort).

So, once again, the corrected line is:
thread.start_new_thread(write, (the_madness,))

Don't forget that because it's a tuple of one element, it has to have the comma after the first element.

I would try this code out, but I don't have a database to test it on, and in all honesty, I can't be bothered. Hope it works though. :)

Allan.