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

[Lee Harr]

In article <fu************ *************** *****@4ax.com>, Daniel Klein wrote:

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
Actually, it returns True, not 'True'
code. So my question is what is the proper method for setting booleans
in 2.3?

Really confused,

True and False are now built in to 2.3
python Python 2.3 (#1, Aug 1 2003, 15:18:54)
[GCC 2.95.4 20020320 [FreeBSD]] on freebsd4
Type "help", "copyright" , "credits" or "license" for more information.

dir(__builtins_ _) ['ArithmeticErro r', 'AssertionError ', 'AttributeError ', 'DeprecationWar ning',
'EOFError', 'Ellipsis', 'EnvironmentErr or', 'Exception',

'False', .snip. 'True', .snip.

'type', 'unichr', 'unicode', 'vars', 'xrange', 'zip']

but I think if you had an up-to-date 2.2 they should have been there too...

python2.2

Python 2.2.3 (#1, Jun 9 2003, 18:01:50)
[GCC 2.95.4 20020320 [FreeBSD]] on freebsd4
Type "help", "copyright" , "credits" or "license" for more information. dir(__builtins_ _)

['ArithmeticErro r', 'AssertionError ', 'AttributeError ', 'DeprecationWar ning',
'EOFError', 'Ellipsis', 'EnvironmentErr or', 'Exception',

'False', .snip. 'True', .snip.

'super', 'tuple', 'type', 'unichr', 'unicode', 'vars', 'xrange', 'zip']


What error are you getting? How are you using true and false?
I know the developers were very careful to not cause any compatibilty
problems with the addition of booleans.

[John Roth]

"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

[John Roth]

"Andrew Dalke" <ad****@mindspr ing.com> wrote in message
news:bg******** **@slb0.atl.min dspring.net...

Daniel Klein:

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

This was at the recommendation of someone on this list some time ago.

John Roth

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.

Indeed, there were no true booleans in Python, but there were
actual PyTrue and PyFalse objects at the C level. Doing the "1 == 1"
trick would expose that implementation choice to Python.

This was rarely used. The only place I know of is in the win32 code,
where a COM API can take a boolean or an integer function. The
win32 interface checks if the value is PyTrue/PyFalse,

Here's relevant links
http://mail.python.org/pipermail/pyt...er/015260.html
http://mailman.pythonpros.com/piperm...q1/000106.html

So, are you saying that this would have returned -1, rather than 1?

John Roth
Andrew
da***@dalkescie ntific.com

[François Pinard]

[Daniel Klein]

So my question is what is the proper method for setting booleans in 2.3?

Hi, Daniel.

In 2.3, you do not need to set booleans, `True' and `False' are just there.

However, if you have a need to write portably against many versions, you
might try something like:

try:
True
except NameError:
False, True = range(2)

in modules where you need to use `True' or `False'.

--
François Pinard http://www.iro.umontreal.ca/~pinard

[Andrew Dalke]

John Roth:

So, are you saying that this would have returned -1, rather than 1?
No, and I don't know how you thought I suggested it. If PyTrue returned
-1 before then "True = (1==1)" would not provide the right compatibility
between different Python versions and so would not be an appropriate
suggestion at all.

You must have misread the text from the second URL
http://mailman.pythonpros.com/piperm...q1/000106.html
in it, Mark Hammond said: The only thing that I can see changing is the literal value of the
boolean field - currently, the conversion from VT_BOOL to integer will
result in 0 or -1. PyTrue is 1

The boolean returned from COM is -1. PyTrue is (and was) 1.

Andrew
da***@dalkescie ntific.com

[Daniel Klein]

On Mon, 04 Aug 2003 02:13:57 GMT, Lee Harr <mi*****@fronti ernet.net>
wrote:

In article <fu************ *************** *****@4ax.com>, Daniel Klein wrote:

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

Actually, it returns True, not 'True'

In this case, it _did_ return a literal string of 'True' cuz I was
using str(true) and str(false). That was the nature of the buglet.
Before str(true) would return return '1' and str(false) would return
'0'. Sorry that I didn't include this bit of information in the
original post :-(

Dan

[Daniel Klein]

On 04 Aug 2003 06:17:37 -0400, pi****@iro.umon treal.ca (François
Pinard) wrote:

[Daniel Klein]

So my question is what is the proper method for setting booleans in 2.3?

Hi, Daniel.

In 2.3, you do not need to set booleans, `True' and `False' are just there.

However, if you have a need to write portably against many versions, you
might try something like:

try:
True
except NameError:
False, True = range(2)

in modules where you need to use `True' or `False'.

Thanks François. I don't need to support multiple versions. I simply
changed the code from:

true = (1 == 1)

to

true = 1

and presto, no more bug :-)

Dan

[Daniel Klein]

On Wed, 06 Aug 2003 09:18:13 +1000, Mark Hammond
<mh******@skipp inet.com.au> wrote:

Daniel Klein wrote:

Thanks François. I don't need to support multiple versions. I simply
changed the code from:

true = (1 == 1)

to

true = 1

and presto, no more bug :-)

For the sake of being pedantic, I believe your code still does have a
bug. You bug is that you rely on the "str()" of a boolean value
returning a specific string. Your code should probably check the bool
and create your own string rather than relying on this behaviour
remaining unchanged forever.

I'm not really taking a str() on a boolean value anymore; it's being
taken on an integer value. Are you saying that...

true = 1
str(true) # this should always return '1' now and forever more

....could cause problems in the future?

The reason I'm taking a str() value is cuz it is being sent over a
socket to a non-python server process, where it is converted back to a
boolean.

Make sense now?

Dan

[Daniel Klein]

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

The reason I'm taking a str() value is cuz it is being sent over a
socket to a non-python server process, where it is converted back to a
boolean.

In that case, you'd be better off converting using your own routine
rather than relying on a particular behaviour of str() for this test.
Basically, do something like

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

and save yourself any further future pain...

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]

Dan