Logical AND question

[3c273]

Hello,
Can someone explain to me why only one of these two if/print statements
prints something? Thanks!
Louis

IDLE 1.0.2[color=blue][color=green][color=darkred]
>>> s = ''
>>> t = ''
>>> if s and t == '':[/color][/color][/color]
print "This doesn't work!"

[color=blue][color=green][color=darkred]
>>> s and t[/color][/color][/color]
''[color=blue][color=green][color=darkred]
>>> if s == '' and t == '':[/color][/color][/color]
print "This does!"


This does![color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

[Tor Iver Wilhelmsen]

Re: Logical AND question

"3c273" <nospam@nospam. com> writes:
[color=blue][color=green][color=darkred]
> >>> if s and t == '':[/color][/color]
> print "This doesn't work!"[/color]

This is really

if (s) and (t == '')

which evaluates to false since "if (s)" returns false for the empty
string.

[Peter Otten]

Re: Logical AND question

Tor Iver Wilhelmsen wrote:
[color=blue]
> "3c273" <nospam@nospam. com> writes:
>[color=green][color=darkred]
>> >>> if s and t == '':[/color]
>> print "This doesn't work!"[/color]
>
> This is really
>
> if (s) and (t == '')
>
> which evaluates to false since "if (s)" returns false for the empty
> string.[/color]

The original poster probably wants
[color=blue][color=green][color=darkred]
>>> if s == t == "":[/color][/color][/color]
.... print "this works"
....
this works[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

or the conventional
[color=blue][color=green][color=darkred]
>>> if s == "" and t == "":[/color][/color][/color]
.... print "but this is more common"
....
but this is more common[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

Peter

[3c273]

Re: Logical AND question

Thank you both :-)

"Peter Otten" <__peter__@web. de> wrote in message
news:c808i3$aen $06$1@news.t-online.com...[color=blue]
> Tor Iver Wilhelmsen wrote:
>[color=green]
> > "3c273" <nospam@nospam. com> writes:
> >[color=darkred]
> >> >>> if s and t == '':
> >> print "This doesn't work!"[/color]
> >
> > This is really
> >
> > if (s) and (t == '')
> >
> > which evaluates to false since "if (s)" returns false for the empty
> > string.[/color]
>
> The original poster probably wants
>[color=green][color=darkred]
> >>> if s == t == "":[/color][/color]
> ... print "this works"
> ...
> this works[color=green][color=darkred]
> >>>[/color][/color]
>
> or the conventional
>[color=green][color=darkred]
> >>> if s == "" and t == "":[/color][/color]
> ... print "but this is more common"
> ...
> but this is more common[color=green][color=darkred]
> >>>[/color][/color]
>
> Peter
>[/color]