[issue25433] whitespace in strip()/lstrip()/rstrip()

[Ulf Rompe]

Change by Ulf Rompe :


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pull_request: https://github.com/python/cpython/pull/14775

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Ulf Rompe]

Change by Ulf Rompe :


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pull_requests: +14564
pull_request: https://github.com/python/cpython/pull/14771

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Ulf Rompe]

Ulf Rompe  added the comment:

Using a re.sub() call as documentation:

1. wouldn't be helpful for many developers. If they need to look up the 
documentation of a simple method they shouldn't be forced to learn about a more 
complex one as well to understand it.
2. would be wild guessing since the re module defines its own whitespace as 
well.

I have created a pull request that aligns the strip methods of bytearray to 
those of bytes objects. The implementation found there is cleaner and even a 
little bit faster.

Current master:

./python -m timeit -s 'bla = bytearray(b"  foo  ")' 'bla.lstrip()'
100 loops, best of 5: 245 nsec per loop
./python -m timeit -s 'bla = bytearray(b"  foo  ")' 'bla.rstrip()'
100 loops, best of 5: 245 nsec per loop
./python -m timeit -s 'bla = bytearray(b"  foo  ")' 'bla.strip()'
100 loops, best of 5: 260 nsec per loop

Using my patch:

./python -m timeit -s 'bla = bytearray(b"  foo  ")' 'bla.lstrip()'
100 loops, best of 5: 235 nsec per loop
./python -m timeit -s 'bla = bytearray(b"  foo  ")' 'bla.rstrip()'
100 loops, best of 5: 235 nsec per loop
./python -m timeit -s 'bla = bytearray(b"  foo  ")' 'bla.strip()'
100 loops, best of 5: 239 nsec per loop


I have also updated the documentation, adding "whitespace" to the glossary and 
linking to it from many places in the documentation of standard types.

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nosy: +rompe

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Roundup Robot]

Change by Roundup Robot :


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keywords: +patch
pull_requests: +14548
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/14753

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Elliot Edmunds]

Elliot Edmunds  added the comment:

Not sure how helpful it would be to have the re.sub expressions for lstrip and 
rstrip, but I think it would look like:

l_stripped = re.sub(r'^\s*', '', foo)
r_stripped = re.sub(r'\s*$', '', foo)

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nosy: +Elliot Edmunds
Added file: https://bugs.python.org/file47769/whitespace_regex.py

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Oliver Urs Lenz]

Oliver Urs Lenz  added the comment:

Slightly tangential, but it would be great if the documentation of lstrip() and 
rstrip() could include an equivalent definition in terms of re.sub(), e.g.:

lstrip(foo) == re.sub(r'(?u)\A\s*', '', foo)
rstrip(foo) == re.sub(r'(?u)\s*\Z', '', foo)

(Or whatever else is correct.)

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nosy: +oulenz

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Jakub Wilk]

Change by Jakub Wilk :


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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Nitish]

Change by Nitish :


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nosy: +nitishch

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Dimitri Papadopoulos Orfanos]

Dimitri Papadopoulos Orfanos  added the comment:

I agree on avoiding a link to str.isspace() and defining "whitespace" instead.

However please note there are many de facto definitions of "whitespace". All of 
them must be documented - or at least the conceptual classes of "whitespace" 
and clarify which class each of the following belongs to:

* Unicode whitespaces are by very far the most common: str.isspace(), 
strip()/lstrip()/rstrip(), Py_UNICODE_ISSPACE.

* Py_ISSPACE targets byte/bytearray but is never used!

* bytearray.strip() does not use Py_ISSPACE but a hardcoded list of ASCII 
whitespaces instead.

* finally string.whitespace is probably equivalent to the list used by 
bytearray.strip().

Beyond the docs, I think Python 3 should rationalize bytearray.strip() /  
Py_ISSPACE / string.whitespace, probably having bytearray.strip() rely on 
Py_ISSPACE, and Py_ISSPACE rely on string.whitespace unless string.whitespace 
is obsoleted.

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Joel Johnson]

Joel Johnson  added the comment:

I have started working on this and will have a pull request submitted by the 
end of the week. 

The term "whitespace" appears in several contextual situations throughout the 
documentation. While all situations would benefit from the definition of 
"whitespace" contained in the str.isspace() documentation, not all of the 
situations would benefit from a link to str.isspace() whose primary goal is to 
document the str.isspace() function and not to provide a global definition of 
what a whitespace character is.

Therefore I suggest the documentation of Python 3 create a new glossary 
definition of "whitespace" (which contains the definition currently in the 
str.isspace() documentation) and is pointed to wherever the term "whitespace" 
is used in any documentation related to strings - including this specific case 
of strip()/lstrip()/rstrip().

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nosy: +joel.johnson

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Cheryl Sabella]

Change by Cheryl Sabella :


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versions: +Python 3.7, Python 3.8 -Python 3.5, Python 3.6

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Dimitri Papadopoulos Orfanos]

Dimitri Papadopoulos Orfanos added the comment:

In Python 3 the situation is similar:
* The Py_UNICODE_ISSPACE macro is used internally to define str.isspace() and 
wherever Python needs to detect "whitespace" characters in strings.
* There is an equivalent function Py_ISSPACE for bytes/bytearray.
* The bytearray.strip() implementation for bytearray relies on hardcoded ASCII 
whitespaces instead of Py_ISSPACE.
* string.whitespace is a list of "ASCII whitespace characters" carved in stone. 
As far as I can see string.whitespace is defined but not used anywhere in 
Python source code.

Therefore I suggest the documentation of Python 3 points to str.isspace() 
wherever the term "whitespace" is used in any documentation related to strings 
- including this specific case of strip()/lstrip()/rstrip().

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Dimitri Papadopoulos Orfanos]

Dimitri Papadopoulos Orfanos added the comment:

In Python 2, as far as I can understand, string.whitespace and str.isspace() 
are different:
* str.isspace() is built upon the C isspace() function and is therefore 
locale-dependant. Python heavily relies on isspace() to detect "whitespace" 
characters.
* string.whitespace is a list of "ASCII whitespace characters" carved in stone. 
As far as I can see string.whitespace is defined but not used anywhere in 
Python source code.

See source code:
* Modules/stringobject.c around line 3319:
  [...]
  string_isspace(PyStringObject *self)
  {
  [...]
  e = p + PyString_GET_SIZE(self);
  for (; p < e; p++) {
  if (!isspace(*p))
  return PyBool_FromLong(0);
  }
  return PyBool_FromLong(1);
  [...]
* Lib/string.py near line 23:
  whitespace = ' \t\n\r\v\f'

Functions strip()/lstrip()/rstrip() use str.isspace() and have nothing to do 
with string.whitespace:

* Modules/stringobject.c around line 1861:
[...]
do_strip(PyStringObject *self, int striptype)
{
[...]
i = 0;
if (striptype != RIGHTSTRIP) {
while (i < len && isspace(Py_CHARMASK(s[i]))) {
i++;
}
}
[...]

Therefore I suggest the documentation of Python 2.7 points to str.isspace() 
wherever the term "whitespace" is used in the documentation - including this 
specific case of strip()/lstrip()/rstrip().

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Ezio Melotti]

Changes by Ezio Melotti :


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keywords: +easy
nosy: +ezio.melotti
stage:  -> needs patch
versions: +Python 3.6

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[issue25433] whitespace in strip()/lstrip()/rstrip()

[Dimitri Papadopoulos Orfanos]

New submission from Dimitri Papadopoulos Orfanos:

The documentation of strip() / lstrip() / rstrip() should define "whitespace" 
more precisely.

The Python 3 documentation refers to "ASCII whitespace" for bytes.strip() / 
bytes.lstrip() / bytes.rstrip() and "whitespace" for str.strip() / str.lstrip() 
/ str.rstrip(). I suggest the following improvements:
* add a link from "ASCII whitespace" to string.whitespace or bytes.isspace(),
* define plain "whitespace" more precisely (possibly with a link to 
str.isspace()).

The Python 2 documentation refers to plain "whitespace". As far as I know 
strip() removes ASCII whitespaces only. If so, please:
* add a link to string.whitespace or str.isspace(),
* improve the string.whitespace documentation and explain that it is 
locale-dependent (see documentation of str.isspace()).

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assignee: docs@python
components: Documentation
messages: 253152
nosy: Dimitri Papadopoulos Orfanos, docs@python
priority: normal
severity: normal
status: open
title: whitespace in strip()/lstrip()/rstrip()
type: enhancement
versions: Python 2.7, Python 3.5

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