append to non-existing list

[Thomas Bellman]

Yves Glodt <y.glodt at sitasoftware.lu> writes:

> I guess that's normal as it's the way python works...?!?

Yes, that's the way Python works.

> My question is: Is there no way to append to a non existing list?

The next time you go shopping at your local super-market, do
*not* get a shopping-cart (or shopping-basket, or any similar
container).  As you pick up the things you want to buy, try
to put them into the non-existing cart.  Perhaps you will then
become enlightened.

> I am lazy for declaring it first, IMHO it bloats the code, and (don't 
> know if it's good to say that here) where I come from (php) I was used 
> to not-needing it...

Basically you want Python to automatically create a list out of
nowhere and bind a variable to that list when you try to access
a variable that doesn't exist in a certain way.  How do you
propose that Python should now that it is a *list* you want, and
not some other kind of object?


There actually is a way to do what you want:

    for row in sqlsth:
	try:
	    pkcolumns.append(row[0].strip())
	except NameError:
	    pkcolumns = [ row[0].strip() ]

However, as you see it is much more work than to do it the right
way.  It's also much more fragile; think for example about what
happens if your SQL statement (I assume that's what sqlsth is)
yields zero rows, and you then try to look at pkcolumns after
that loop.


-- 
Thomas Bellman,   Lysator Computer Club,   Linköping University,  Sweden
"God is real, but Jesus is an integer."      !  bellman @ lysator.liu.se
                                             !  Make Love -- Nicht Wahr!