[issue22843] doc error: 6.2.4. Match Objects

[Irit Katriel]

Change by Irit Katriel :


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resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue22843] doc error: 6.2.4. Match Objects

[Terry J. Reedy]

Terry J. Reedy added the comment:

David is correct that the current phrasing is correct.  The phase 'x has a 
boolean value of True' means 'bool(x) is True', which is always true for match 
objects, as well as for non-zero numbers, non-empty collections, and many other 
things.  This does *not* imply equality between the object and its boolean 
value.  In fact, nearly all objects are not equal to their boolean value.  
Clayton could just as well as have written blah = 'a' or blah = 1 + 1j and 
gotten the name non-surprising result.

There is nothing special about boolean values in this respect.  The string 
value of x is str(x) and in general, x != str(x).  (This also sometimes 
confuses people.)  Similarly, if x has an integral value int(x), it does not 
necessarily equal that value: int(3.1459) != 3.

I think the doc is fine as is.  The fact that 3 is considered to be '3' in a 
display context does not mean that we do not write the string value of 3 is 
'3'.  It is fundamental to Python that essentially all objects o have a string 
value str(o) and a boolean value bool(o) and that those mappings are sometimes 
used automatically for display and logic.

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nosy: +terry.reedy

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[issue22843] doc error: 6.2.4. Match Objects

[Clayton Kirkwood]

Clayton Kirkwood added the comment:

Cool

-Original Message-
From: Terry J. Reedy [mailto:rep...@bugs.python.org]
Sent: Friday, November 14, 2014 1:04 PM
To: c...@godblessthe.us
Subject: [issue22843] doc error: 6.2.4. Match Objects


Terry J. Reedy added the comment:

David is correct that the current phrasing is correct.  The phase 'x has
a boolean value of True' means 'bool(x) is True', which is always true
for match objects, as well as for non-zero numbers, non-empty
collections, and many other things.  This does *not* imply equality
between the object and its boolean value.  In fact, nearly all objects
are not equal to their boolean value.  Clayton could just as well as
have written blah = 'a' or blah = 1 + 1j and gotten the name non-
surprising result.

There is nothing special about boolean values in this respect.  The
string value of x is str(x) and in general, x != str(x).  (This also
sometimes confuses people.)  Similarly, if x has an integral value
int(x), it does not necessarily equal that value: int(3.1459) != 3.

I think the doc is fine as is.  The fact that 3 is considered to be '3'
in a display context does not mean that we do not write the string
value of 3 is '3'.  It is fundamental to Python that essentially all
objects o have a string value str(o) and a boolean value bool(o) and
that those mappings are sometimes used automatically for display and
logic.

--
nosy: +terry.reedy

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[issue22843] doc error: 6.2.4. Match Objects

[Ben Finney]

Ben Finney added the comment:

The current wording of the passage “Match objects always have a boolean value 
of True” implies that the value compares equal to the ‘True’ constant. That 
implication is incorrect.

I disagree with R. David Murray; if we want to say that a value is considered 
true *in a boolean context*, that's very different from saying it has the 
“True” value.

Georg, “evaluates true in a boolean context” has the meaning you're seeking; it 
is chosen precisely because it does *not* imply equality to the True constant.

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[issue22843] doc error: 6.2.4. Match Objects

[Georg Brandl]

Georg Brandl added the comment:

evaluates true should not be used in any case, the objects do not equal to 
True in any case.

The phrase is considered true in a boolean context is already in the docs and 
could be used here too.

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[issue22843] doc error: 6.2.4. Match Objects

[Clayton Kirkwood]

New submission from Clayton Kirkwood:

Documentation says:
 Match objects always have a boolean value of True. Since match() and
 search() return None when there is no match, you can test whether 
 there was a match with a simple if statement:

 match = re.search(pattern, string)
 if match:
 process(match)

What happens:
blah = _sre.SRE_Match object; span=(0, 28), match='BRNov. 10, 08:16:09 PM 
EST'
 if blah == True:
   print(True)
 if blah:
print('blah True')

blah True
///

Blah is not True

One suggestion: instead, the passage above should say “evaluates true in a 
boolean context”.

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assignee: docs@python
components: Documentation
messages: 230994
nosy: crkirkwood, docs@python
priority: normal
severity: normal
status: open
title: doc error: 6.2.4. Match Objects
type: resource usage
versions: Python 3.4

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[issue22843] doc error: 6.2.4. Match Objects

[R. David Murray]

R. David Murray added the comment:

That's what have a boolean value of True means.  (ie: bool(matchobject) is 
True).  I'm neutral on whether or not it is worth changing the wording.

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nosy: +r.david.murray
type: resource usage - behavior

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