Bugs item #1361643, was opened at 2005-11-19 20:02
Message generated for change (Comment added) made by birkenfeld
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 6
Submitted By: Steven Bethard (bediviere)
Assigned to: Greg Ward (gward)
Summary: textwrap.dedent() expands tabs
Initial Comment:
I'm not sure whether this is a documentation bug or a
code bug, but textwrap.dedent() expands tabs (and
AFAICT doesn't give the user any way of stopping this):
py> def test():
... x = ('abcd efgh\n'
... 'ijkl mnop\n')
... y = textwrap.dedent('''... abcd efgh
... ijkl mnop
... ''')
... return x, y
...
py> test()
('abcd\tefgh\nijkl\tmnop\n', 'abcd efgh\nijkl
mnop\n')
Looking at the code, I can see the culprit is the first
line:
lines = text.expandtabs().split('\n')
If this is the intended behavior, I think the first
sentence in the documentation[1] should be replaced with:
"""
Replace all tabs in string with spaces as per
str.expandtabs() and then remove any whitespace that
can be uniformly removed from the left of every line in
text.
"""
and (I guess this part is an RFE) textwrap.dedent()
should gain an optional expandtabs= keyword argument to
disable this behavior.
If it's not the intended behavior, I'd love to see that
.expandtabs() call removed.
[1]http://docs.python.org/lib/module-textwrap.html
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>Comment By: Reinhold Birkenfeld (birkenfeld)
Date: 2005-12-15 09:45
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Looks good!
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Comment By: Raymond Hettinger (rhettinger)
Date: 2005-11-20 07:04
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Suggested code:
import re as _re
_emptylines_with_spaces = _re.compile('(?m)^[ \t]+$')
_prefixes_on_nonempty_lines = _re.compile('(?m)(^[
\t]*)(?:[^ \t\n]+)')
def dedent(text):
text = _emptylines_with_spaces.sub('', text)
prefixes = _prefixes_on_nonempty_lines.findall(text)
margin = min(prefixes or [''])
if margin:
text = _re.sub('(?m)^' + margin, '', text)
return text
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Comment By: Raymond Hettinger (rhettinger)
Date: 2005-11-20 05:52
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After more thought, I think the expandtabs() is a bug since
it expands content tabs as well as margin tabs:
>>> textwrap.dedent('\tABC\t\tDEF')
'ABC DEF'
This is especially problematic given that dedent() has to
guess at the tab size.
If this gets fixed, I recommend using regular expressions as
a way to indentify common margin prefixes on non-empty
lines. This will also mixes of spaces and tabs without
altering content with embedded tabs and without making
assumptions about the tab size. Also, it ought to run
somewhat faster.
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Comment By: Raymond Hettinger (rhettinger)
Date: 2005-11-19 21:18
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FWIW, the tab expansion would be more useful if the default
tabsize could be changed.
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