getting an empty tuple

**Peter Decker** · Jul 31 '05, 03:55 PM

Re: getting an empty tuple

On 31 Jul 2005 08:40:26 -0700, nephish@xit.net <nephish@xit.ne t> wrote:
[color=blue]
> how do i encorporate that into an equation ?
> i have tried all kinds of stuff
>
> if x == 0L
> if x(0) == None
> if x == None
>
> anyway, what shoud i do to test if the result is empty?[/color]

Just like any other test:

if not x:

--

# p.d.

**Steven D'Aprano** · Jul 31 '05, 04:35 PM

Re: getting an empty tuple

On Sun, 31 Jul 2005 08:40:26 -0700, nephish wrote:
[color=blue]
> Hey there,
> i have a simple database query that returns as a tuple the number of
> rows that the query selected.
> kinda like this
>[color=green][color=darkred]
>>>> cursor.execute( 'select value from table where autoinc > 234')
>>>> x = cursor.fetchall ()
>>>> print x[/color][/color]
>[color=green][color=darkred]
>>>> 21L[/color][/color][/color]

21L is not a tuple, it is a long integer.
[color=blue]
> ok, means 21 rows met the criteria of the query. but if there are none
> that match,
> like i do a
>[color=green][color=darkred]
>>>> print x
>>>> 0L[/color][/color]
>
> how do i encorporate that into an equation ?
> i have tried all kinds of stuff[/color]

And did they work? If they didn't work, tell us the exact error message
you got.

[color=blue]
> if x == 0L[/color]

If x is a long integer, then that will work. Of just "if x == 0:" will
work too.

[color=blue]
> if x(0) == None[/color]

No. That means x is a function, and you are giving it an argument of 0,
and it returns None.
[color=blue]
> if x == None[/color]

You said that your query returns a tuple, but then gave an example where
it returns a long int. None is not a tuple, nor a long int, so testing
either of those things against None will never be true.

Did you try any of these things in the interactive interpreter? Python is
a great language for experimenting, because you can try this yourself:

# run your setup code ...
# and then do some experimenting
cursor.execute( 'select value from table where autoinc > 99999999')
# or some value that will never happen
x = cursor.fetchall ()
print x

What do you get?

[color=blue]
> anyway, what shoud i do to test if the result is empty?[/color]

Long ints are never empty, but they can be zero:

if x == 0:
print "no rows were found"
elif x == 1:
print "1 row was found"
else:
print "%d rows were found" % x

Tuples can be empty:

if len(x) == 0:
print "no rows were found"

or if you prefer:

if x == ():
print "no rows were found"

But the cleanest, most Pythonic way is just to do a truth-test:

if x:
print "something was found"
else:
print "x is empty, false, blank, nothing..."

--
Steven.

**nephish@xit.net** · Jul 31 '05, 06:55 PM

Re: getting an empty tuple

ok, this is what works:
if x == ():

sorry about the bad info. and what i ment to put was
x[0] not x(0)

thanks for the tips
its all good now

shawn

Steven D'Aprano wrote:[color=blue]
> On Sun, 31 Jul 2005 08:40:26 -0700, nephish wrote:
>[color=green]
> > Hey there,
> > i have a simple database query that returns as a tuple the number of
> > rows that the query selected.
> > kinda like this
> >[color=darkred]
> >>>> cursor.execute( 'select value from table where autoinc > 234')
> >>>> x = cursor.fetchall ()
> >>>> print x[/color]
> >[color=darkred]
> >>>> 21L[/color][/color]
>
> 21L is not a tuple, it is a long integer.
>[color=green]
> > ok, means 21 rows met the criteria of the query. but if there are none
> > that match,
> > like i do a
> >[color=darkred]
> >>>> print x
> >>>> 0L[/color]
> >
> > how do i encorporate that into an equation ?
> > i have tried all kinds of stuff[/color]
>
> And did they work? If they didn't work, tell us the exact error message
> you got.
>
>[color=green]
> > if x == 0L[/color]
>
> If x is a long integer, then that will work. Of just "if x == 0:" will
> work too.
>
>[color=green]
> > if x(0) == None[/color]
>
> No. That means x is a function, and you are giving it an argument of 0,
> and it returns None.
>[color=green]
> > if x == None[/color]
>
> You said that your query returns a tuple, but then gave an example where
> it returns a long int. None is not a tuple, nor a long int, so testing
> either of those things against None will never be true.
>
> Did you try any of these things in the interactive interpreter? Python is
> a great language for experimenting, because you can try this yourself:
>
> # run your setup code ...
> # and then do some experimenting
> cursor.execute( 'select value from table where autoinc > 99999999')
> # or some value that will never happen
> x = cursor.fetchall ()
> print x
>
> What do you get?
>
>[color=green]
> > anyway, what shoud i do to test if the result is empty?[/color]
>
> Long ints are never empty, but they can be zero:
>
> if x == 0:
> print "no rows were found"
> elif x == 1:
> print "1 row was found"
> else:
> print "%d rows were found" % x
>
> Tuples can be empty:
>
> if len(x) == 0:
> print "no rows were found"
>
> or if you prefer:
>
> if x == ():
> print "no rows were found"
>
>
> But the cleanest, most Pythonic way is just to do a truth-test:
>
> if x:
> print "something was found"
> else:
> print "x is empty, false, blank, nothing..."
>
>
> --
> Steven.[/color]

getting an empty tuple

getting an empty tuple

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