variable assignment in "while" loop

Re: variable assignment in "while&quo t; loop

Sybren Stuvel wrote:[color=blue]
>
> 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.fetc hone():
> print "Informatio n: "+str(info)
>
> comes to mind. Unfortunately, this doesn't work. Is there a similar
> construct in python?[/color]

Yes:

while 1:
info = mydbcursor.fetc hone()
if not info:
break
print "Informatio n: " + str(info)

-Peter

Re: variable assignment in "while&quo t; loop

In article <slrnbicoqq.6gh .sybrenUSE@sybr en.thirdtower.c om>,
Sybren Stuvel <sybrenUSE@YOUR thirdtower.imag ination.com> wrote:[color=blue]
>
>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.fetc hone():
> print "Informatio n: "+str(info)
>
>comes to mind. Unfortunately, this doesn't work. Is there a similar
>construct in python?[/color]

Peter usually gives a good answer, but this time there's a better
answer:

def fetch_iter(curs or):
info = True
while info:
info = cursor.fetchone ()
yield info

for info in fetch_iter(mydb cursor):
print "Informatio n:" + str(info)

Generally speaking, any time you want to do assignment as part of a
while loop, you really want to convert it a for loop.

BTW, DO NOT USE TABS in Python programs. You WILL regret it.
--
Aahz (aahz@pythoncra ft.com) <*> http://www.pythoncraft.com/

This is Python. We don't care much about theory, except where it intersects
with useful practice. --Aahz

Re: variable assignment in &quot;while&quo t; loop

"Aahz" <aahz@pythoncra ft.com> wrote:[color=blue]
>
> Peter usually gives a good answer, but this time there's a better
> answer:[/color]

With a bug, but if we combine Peter's answer with yours we get an
even better answer:

def fetch_iter(mydb cursor):
while 1:
info = mydbcursor.fetc hone()
if not info:
break
yield info

- Anders

Re: variable assignment in &quot;while&quo t; loop


Sybren> Is it possible to use an assignment in a while-loop?

Nope. To learn why, read question 6.30 of the FAQ:



Skip

Re: variable assignment in &quot;while&quo t; loop

Sybren Stuvel wrote:[color=blue]
> while info = mydbcursor.fetc hone():
> print "Informatio n: "+str(info)[/color]

Gustavo has already pointed out the classic Pythonic ways of writing
this. In the general case, where you don't have an iterator handed to
you, you can make one as of Python 2.2 like so:

def each(f):
'''Make a zero-argument function or method iterable.
It had better have side effects, or this is pointless.'''
v = f()
while v:
yield v
v = f()

for info in each(mydbcursor .fetchone):
print "Informatio n:", info

Of course, all this really does is to factor out one of the classic
Pythonic patterns into a wrapper function.

There's also the Pita pocket solution:

class Pita(object):
__slots__ = ('pocket',)
marker = object()
def __init__(self, v=marker):
if v is not self.marker:
self.pocket = v
def __call__(self, v=marker):
if v is not self.marker:
self.pocket = v
return self.pocket

p = Pita(10)
while p(p() - 1):
print p()

Cheers,

Evan @ 4-am

Re: variable assignment in &quot;while&quo t; loop

On 29 Jul 2003 12:08:50 GMT, Sybren Stuvel <sybrenUSE@YOUR thirdtower.imag ination.com> wrote:
[color=blue]
>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.fetc hone():
> print "Informatio n: "+str(info)
>
>comes to mind. Unfortunately, this doesn't work. Is there a similar
>construct in python?
>[/color]
I thought of a little variation on the list comprehension hack that is usually advised against:

while [info for info in [mydbcursor.fetc hone()] if info]:
print "Informatio n: %s" % info

I sort of like the mnemonic of the if info that makes the while
see [] at the end rather than e.g. [None][0]

Regards,
Bengt Richter