On 9/14/2016 8:05 AM, Jussi Piitulainen wrote:
Serhiy Storchaka writes:
On 14.09.16 11:28, Steven D'Aprano wrote:
I'm not sure if it makes sense to talk about an "empty regular
expression", or if that is the same as re.compile(''). Presumably if
such a thing makes sense, it would match nothing, from any input at
all.
Actually, it matches anything. re.compile('').match(x) returns
non-false value for any valid x.
It matches the empty string. The .match method returns a match object if
the regex matches at the start of the input. See span:
re.compile('').match('foo')
===> <_sre.SRE_Match object; span=(0, 0), match=''>
There's an empty string at every position, same content, different span:
re.compile('').findall('foo')
===> ['', '', '', '']
To put it slightly differently, regexes match slices. A string of n
chars has n+1 empty (len 0) slices - the 2 at the ends and the n-1
between chars.
--
Terry Jan Reedy
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