Il giorno domenica 8 maggio 2016 18:16:56 UTC+2, Peter Otten ha scritto:
> Sergio Spina wrote:
>
> > In the following ipython session:
> >
> >> Python 3.5.1+ (default, Feb 24 2016, 11:28:57)
> >> Type "copyright", "credits" or "license" for more information.
> >>
> >> IPython 2.3.0 -- An enhanced Interactive Python.
> >>
> >> In [1]: import re
> >>
> >> In [2]: patt = r""" # the match pattern is:
> >> ...: .+ # one or more characters
> >> ...: [ ] # followed by a space
> >> ...: (?=[@#D]:) # that is followed by one of the
> >> ...: # chars "@#D" and a colon ":"
> >> ...: """
> >>
> >> In [3]: pattern = re.compile(patt, re.VERBOSE)
> >>
> >> In [4]: m = pattern.match("Jun at i Bun#i @:Janji")
> >>
> >> In [5]: m.group()
> >> Out[5]: 'Jun at i Bun#i '
> >>
> >> In [6]: m = pattern.match("Jun at i Bun#i @:Janji D:Banji")
> >>
> >> In [7]: m.group()
> >> Out[7]: 'Jun at i Bun#i @:Janji '
> >>
> >> In [8]: m = pattern.match("Jun at i Bun#i @:Janji D:Banji #:Junji")
> >>
> >> In [9]: m.group()
> >> Out[9]: 'Jun at i Bun#i @:Janji D:Banji '
> >
> > Why the regex engine stops the search at last piece of string?
> > Why not at the first match of the group "@:"?
> > What can it be a regex pattern with the following result?
> >
> >> In [1]: m = pattern.match("Jun at i Bun#i @:Janji D:Banji #:Junji")
> >>
> >> In [2]: m.group()
> >> Out[2]: 'Jun at i Bun#i '
>
> Compare:
>
> >>> re.compile("a+").match("aaaa").group()
> 'aaaa'
> >>> re.compile("a+?").match("aaaa").group()
> 'a'
>
> By default pattern matching is "greedy" -- the ".+" part of your regex
> matches as many characters as possible. Adding a ? like in ".+?" triggers
> non-greedy matching.
> In [2]: patt = r""" # the match pattern is:
> ...: .+ # one or more characters
> ...: [ ] # followed by a space
> ...: (?=[@#D]:) # ONLY IF is followed by one of the <<< please note
> ...: # chars "@#D" and a colon ":"
> ...: """
>From the python documentation
> (?=...)
> Matches if ... matches next, but doesn't consume any of the string.
> This is called a lookahead assertion. For example,
> Isaac (?=Asimov) will match 'Isaac ' only if it's followed by 'Asimov'.
I know about greedy and not-greedy, but the problem remains.