True

[Daniel Klein]

In Python 2.2 I use to have

true = (1 == 1)
false = not true

This was at the recommendation of someone on this list some time ago.
The reason (if I remember correctly) was that setting

true = 1
false = 0

were not true booleans.

Now the expression (1 == 1) returns 'True', and caused a bug in my
code. So my question is what is the proper method for setting booleans
in 2.3?

Really confused,

Daniel Klein

[Terry Reedy]

"Daniel Klein" <da*****@aracne t.com> wrote in message
news:vr******** *************** *********@4ax.c om...

On Wed, 06 Aug 2003 12:18:45 -0400, Peter Hansen <pe***@engcorp. com>
wrote:

def boolean2String( boolVal):
return { False : '1', True : '0' } [ not boolVal ]

Thanks Peter, that will do the trick. Just wondering though why you
chose to code the opposite values and not as

def boolean2String( boolVal):
return {True:'1', False:'0'}[boolVal]

Your function requires the arg to be 0/1 (True/False). Peter's
function works for *any* input that can be 'not'ed.

TJR

[Martin v. Löwis]

Peter Hansen <pe***@engcorp. com> writes:

As Skip said... but it should have had a comment anyway, since it
wasn't clear. You could also consider using "not not boolVal" if
you want to make the code _slightly_ (IMHO) more readable, and slightly
slower, but I think one still needs a comment explaining it. :-(

I find

def boolean2str(val ):
if val:
return '1'
else:
return '0'

both more readable, and twice as fast. It doesn't need to create a
dictionary each time, and it does not to perform a dictionary lookup.
If you prefer compactness, use

def boolean2str(val , results=('1', '0')):
return results[not val]

Regards,
Martin

[Terry Reedy]

"Martin v. Löwis" <ma****@v.loewi s.de> wrote in message
news:m3******** ****@mira.infor matik.hu-berlin.de...

If you prefer compactness, use

def boolean2str(val , results=('1', '0')):
return results[not val]

-or, more safely (no default arg to accidently overwrite)-

def boolean2str(val ):
return val and '1' or '0'

But one might want the flexibility of intentionally replacing the
results default, as in

print boolean2str(som evalue, ('T', 'F'))

Terry J. Reedy

[Paul Watson]

"John Roth" <ne********@jhr othjr.com> wrote in message
news:vi******** ****@news.super news.com...

"Daniel Klein" <da*****@aracne t.com> wrote in message
news:fu******** *************** *********@4ax.c om...

In Python 2.2 I use to have

true = (1 == 1)
false = not true

This was at the recommendation of someone on this list some time ago.
The reason (if I remember correctly) was that setting

true = 1
false = 0

were not true booleans.
There were no true booleans in 2.2 and earlier. Whoever recommended
that didn't know what he was talking about. There was no difference.

Now the expression (1 == 1) returns 'True', and caused a bug in my
code. So my question is what is the proper method for setting booleans
in 2.3?

I presume what broke your code was depending on the return from
either str() or repr(), or the % operator. That was, unfortunately, one
of the incompatibilite s between 2.2 and 2.3.

In 2.3, Boolean is a subtype of Int, and has two values: True and False.
Both of these are built in constants, so just use them. That's what

they're for. For most purposes, the are the same as 1 and 0, except for what they
return from str() and repr(), and how they get formatted with %.

John Roth

Really confused,

Daniel Klein

Then, what is the best way to write boolean operations for Python 2.1 so
that it will be as 2.3+ ready as possible?

Should we just use 0 and 1?

Until the vendor of the tool we are using delivers a more recent version of
Python with the product, we must produce 2.1 compatible code.

Thanks.

[David Eppstein]

In article <3f**********@t hemost.net>,
"Paul Watson" <pw*****@redlin ec.com> wrote:

Then, what is the best way to write boolean operations for Python 2.1 so
that it will be as 2.3+ ready as possible?

I've been including the following at the start of some of my code:

if 'True' not in globals():
globals()['True'] = not None
globals()['False'] = not True

My hope is that setting up True and False in this convoluted way will
allow it to continue to work in some future version where assignment to
builtins is disallowed.

--
David Eppstein http://www.ics.uci.edu/~eppstein/
Univ. of California, Irvine, School of Information & Computer Science

[Andrew Bennetts]

On Sun, Oct 19, 2003 at 08:17:15AM -0700, David Eppstein wrote:

In article <3f**********@t hemost.net>,
"Paul Watson" <pw*****@redlin ec.com> wrote:

Then, what is the best way to write boolean operations for Python 2.1 so
that it will be as 2.3+ ready as possible?

I've been including the following at the start of some of my code:

if 'True' not in globals():
globals()['True'] = not None
globals()['False'] = not True

Why not simply:

try:
True
except NameError:
True = (1 == 1) # or not None, if you prefer
False = not True

Or were you trying to change the __builtins__ by using globals()?

-Andrew.

[Duncan Booth]

David Eppstein <ep******@ics.u ci.edu> wrote in news:eppstein-
D2************* ******@news.ser vice.uci.edu:

Then, what is the best way to write boolean operations for Python 2.1 so
that it will be as 2.3+ ready as possible?

I've been including the following at the start of some of my code:

if 'True' not in globals():
globals()['True'] = not None
globals()['False'] = not True

My hope is that setting up True and False in this convoluted way will
allow it to continue to work in some future version where assignment to
builtins is disallowed.

Since True will never be in globals unless you assign it there, you might
as well just drop the if statement altogether. Also I fail to see what
benefit you gain from the contorted assignment into the globals dictionary.
Why not just write:

True = not None
False = not True

It has the same effect overall.

If you want to avoid hiding the builtin True and False, then use try..catch
to detect them.

--
Duncan Booth du****@rcp.co.u k
int month(char *p){return(1248 64/((p[0]+p[1]-p[2]&0x1f)+1)%12 )["\5\x8\3"
"\6\7\xb\1\x9\x a\2\0\4"];} // Who said my code was obscure?

[Peter Otten]

Andrew Bennetts wrote:

On Sun, Oct 19, 2003 at 08:17:15AM -0700, David Eppstein wrote:

In article <3f**********@t hemost.net>,
"Paul Watson" <pw*****@redlin ec.com> wrote:

> Then, what is the best way to write boolean operations for Python 2.1
> so that it will be as 2.3+ ready as possible?

I've been including the following at the start of some of my code:

if 'True' not in globals():
globals()['True'] = not None
globals()['False'] = not True

Why not simply:

try:
True
except NameError:
True = (1 == 1) # or not None, if you prefer
False = not True

Or were you trying to change the __builtins__ by using globals()?

-Andrew.

I suppose David tries to avoid a syntax error raised by the assignment

True = somethingElse

in a future version of Python. Therefore he has "hidden" the builtins to be
assigned from the compiler by turning them into strings.

Peter

[David Eppstein]

In article <bn************ *@news.t-online.com>,
Peter Otten <__*******@web. de> wrote:

I suppose David tries to avoid a syntax error raised by the assignment

True = somethingElse

in a future version of Python. Therefore he has "hidden" the builtins to be
assigned from the compiler by turning them into strings.

Yes, exactly.

--
David Eppstein http://www.ics.uci.edu/~eppstein/
Univ. of California, Irvine, School of Information & Computer Science