New submission from Chris Jerdonek:
While working on issue 1859, I found that textwrap.wrap() returns an empty list
when passed the empty string:
>>> from textwrap import wrap
>>> wrap('')
[]
as opposed to a list containing the empty string which is what I expected--
['']
I originally accepted this as intended behavior, but for the following reasons
I now think it is a bug that we should consider fixing:
1. The textwrap documentation says that wrap(), "Wraps the single paragraph in
text (a string) so every line is at most width characters long. Returns a list
of output lines, without final newlines." The empty string is less than width
characters long, so following the documentation, wrapping should not change it.
2. It is known that wrap() is broken for strings containing newlines (i.e.
strings containing more than one paragraph). Indeed, this is the issue that
issue 1859 is meant to fix.
The commonly recommended work-around is to call splitlines() on the incoming
string, pass the pieces to wrap(), and then join the return values on newlines.
However, the behavior described in this issue causes this workaround not to
behave sensibly when the original string contains breaks between paragraphs.
See this message, for example:
http://bugs.python.org/issue1859#msg166627
Currently, this work-around would return "a\nb" for both "a\nb" and "a\n\nb"
for example when common sense says it should preserve the newlines and return
"a\nb" and "a\n\nb", respectively.
3. In addition, the behavior causes the following inconsistent behavior:
>>> repr(wrap(' ', drop_whitespace=False))
"[' ']"
>>> repr(wrap(' ', drop_whitespace=True))
'[]'
The documentation says this about drop_whitespace: "If true, whitespace that,
after wrapping, happens to end up at the beginning or end of a line is
dropped." If the first case is correct, then, the second case should at least
return a non-empty list because that is what would result from dropping
whitespace from the string ' ' in the first list. This is how drop_whitespace
behaves when the string contains non-whitespace characters:
>>> repr(wrap('a ', drop_whitespace=False))
"['a ']"
>>> repr(wrap('a ', drop_whitespace=True))
"['a']"
4. There is no unit test for the case of the empty string, and existing tests
still pass after fixing the issue.
If we cannot correct this behavior, then I feel we should at least document the
inconsistent behavior, and then work around it in the fix for issue 1859.
Marking for this issue to be resolved either way before fixing issue 1859. I
am happy to prepare the patch.
----------
messages: 166940
nosy: cjerdonek
priority: normal
severity: normal
status: open
title: textwrap.wrap('') returns empty list
type: behavior
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue15510>
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