"string".split behaviour for empty strings

[meyarivan]

BPO	811604
Nosy	@rhettinger, @terryjreedy

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2004-03-21.17:11:10.000>
created_at = <Date 2003-09-24.08:20:19.000>
labels = ['interpreter-core']
title = '"string".split behaviour for empty strings'
updated_at = <Date 2004-03-21.17:11:10.000>
user = 'https://bugs.python.org/meyarivan'

bugs.python.org fields:

activity = <Date 2004-03-21.17:11:10.000>
actor = 'nbastin'
assignee = 'none'
closed = True
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2003-09-24.08:20:19.000>
creator = 'meyarivan'
dependencies = []
files = []
hgrepos = []
issue_num = 811604
keywords = []
message_count = 6.0
messages = ['18312', '18313', '18314', '18315', '18316', '18317']
nosy_count = 4.0
nosy_names = ['rhettinger', 'terry.reedy', 'nbastin', 'meyarivan']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue811604'
versions = []

[meyarivan]

"".split() -> []

"".split(' ') -> ['']

It is not clear from the documentation as to what is
the defined behaviour in the above case. To say the
least, it is
completely counter-intuitive..(splitting an empty
string should
return the list [''] in both cases).

From stringobject.c, the behaviour of split_whitespace
(i.e split called without sep) and string_split (split
called with sep) is different for empty
strings..perhaps the function split_whitespace needs to
be patched.

[meyarivan]

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"".split(None) -> []

which is expected because in the case when no sep is
specified and when sep == None, split_whitespace is called..

[rhettinger]

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And so it is. The whitespace version (no args) and the
specified separator version work differently -- the second
version can never return an empty list.

This code has been around for a good while and it is likely
that much code relies on the behavior, so I recommend
classifying it as a beauty spot and closing the bug.

"One man's bug is another man's feature"

[meyarivan]

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Thats so counter intuitive.. :-(

At least the documentation should specify the fact that the
behaviour of "string".split for empty strings is so and so....

The reason this probably never came up ( or mostly ignored
by majority ) is that people probably check if the string is
empty before proceeding to process it..

I am not closing the bug before the specific behaviour of
"string".split for empty strings gets to the docs..

[terryjreedy]

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Suggestion: find section of Lib Ref discussing str.split, quote
existing def, and add succinct sentence that you think is
needed. Then change category to 'documentation' so
appropriate person(s) will see proposal.

[nbastin]

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Fixed in doc/lib/libstring.tex version 1.57