variable assignment in "while" loop

[Andy Todd]

sismex01 at hebmex.com wrote:
>>From: Sybren Stuvel [mailto:sybrenUSE at YOURthirdtower.imagination.com] 
>>Sent: Martes, 29 de Julio de 2003 07:09 a.m.
>>
>>Hi there,
>>
>>Is it possible to use an assignment in a while-loop? I'd like to do
>>something like "loop while there is still something to be read, and if
>>there is, put it in this variable". I've been a C programmer since I
>>was 14, so a construct like:
>>
>>while info = mydbcursor.fetchone():
>>	print "Information: "+str(info)
>>
>>comes to mind. Unfortunately, this doesn't work. Is there a similar
>>construct in python?
>>
>>Sybren
>>
> 
> 
> Well, you say you've programmed C since 14, but not how old you
> are now, so... you could be programming C for six months if you're
> 14-and-a-half ;-)
> 
> Assignment, in Python, is not an expression, it's a statement;
> it doesn't "return" any value, it binds an object's reference
> to a name.  Multiple chained assignments in Python don't work
> the same way as they do in C, because in Python they're merely
> syntactic sugar so you don't have to type them by hand.
> 
> Anyhow... the best way to do what you wanna is simply:
> 
> while 1:
>     info = mydbcursor.fetchone()
>     if not info: break
>     print "Information:", info
> 
> a-ha! you say; yes, the "print" statement ("STATEMENT", not function)
> automagically applies str() to the given object, so if you directly
> print an object, you don't have to str() it, print does that for
> you.
> 
> "But it's so cumbersome" you think, looking upon an inconditional-
> turned-conditional loop.  Don't worry, it'll become natural with
> practice, and after a bit you'll recall your previous C loops
> and think "ewww".  Why?  Because, the C compiler is doing
> exactly that, only implicitly, and hiding it from you.
> That's bad.
> 
> You could also:
> 
> info = mydbcursor.fetchone()
> while info:
>     print "Information:", info
>     info = mydbcursor.fetchone()
> 
> and there's nothing wrong with this; the only "anti-aesthetic"
> thing here is the duplicated line which assigns to "info",
> but that's small potatos, really; don't worry about that.
> 
> Another way, with more modern versions of Python, is to
> iterate directly over the cursor:
> 
> for info in mydbcursor:
>     print "Information:", info
> 
> Why?  Because cursors, if I recall correctly, are iterable
> objects, so you can iterate through them using for: or any
> other similar construct.
> 
> Welcome to programming bliss :-)
> 
> -gustavo
> 
> 

Spot on, with one (minor) correction. With a for loop you have to 
iterate over the results of a call to a method on the cursor, e.g.;

for info in mydbcursor.fetchall():
     print "Information:", info

You could replace fetchall() with fetchmany() or, if you are feeling 
contrary, fetchone() ;-)

Regards,
Andy
-- 
--------------------------------------------------------------------------------
 From the desk of Andrew J Todd esq - http://www.halfcooked.com/