python - Named regular expression group "(?Pregexp)": what does "P" stand for?

itemprop="text">

In Python, the
(?P…) href="http://docs.python.org/library/re.html#regular-expression-syntax"
rel="noreferrer">syntax allows one to refer to the matched string through
its name:

>>>
            import re
>>> match = re.search('(?P.*)
            (?P.*)', 'John 123456')
>>>
            match.group('name')
'John'

What
does "P" stand for? I could not find any hint in the href="http://docs.python.org/library/re.html#regular-expression-syntax"
rel="noreferrer">official
documentation.

I would love to get
ideas about how to help my students remember this syntax. Knowing what "P" does stand
for (or might stand for) would be useful.

class="post-text" itemprop="text">

class="normal">Answer

Since we're all guessing, I might
as well give mine: I've always thought it stood for Python. That may sound pretty stupid
-- what, P for Python?! -- but in my defense, I vaguely remembered href="http://markmail.org/message/oyezhwvefvotacc3">this thread [emphasis
mine]:

Subject:
Claiming (?P...) regex syntax extensions

From:
Guido van Rossum (gui...@CNRI.Reston.Va.US)

Date: Dec 10, 1997 3:36:19 pm

I have
an unusual request for the Perl developers (those that develop

the
Perl language). I hope this (perl5-porters) is the right list. I
am cc'ing
the Python string-sig because it is the origin of most of
the work I'm
discussing here.

You are probably aware of
Python. I am Python's creator; I am
planning to release a next "major"
version, Python 1.5, by the end of
this year. I hope that Python and Perl can
co-exist in years to come;
cross-pollination can be good for both languages.
(I believe Larry
had a good look at Python when he added objects to Perl 5;
O'Reilly
publishes books about both
languages.)

As you may know, Python
1.5 adds a new regular expression module that
more closely matches Perl's
syntax. We've tried to be as close to the
Perl syntax as possible within
Python's syntax. However, the regex
syntax has some Python-specific
extensions, which all begin with (?P .
Currently there are two of
them:

(?P...) Similar to regular grouping
parentheses, but the text
matched by the group is accessible after the match
has been performed,
via the symbolic group name "foo".

(?P=foo) Matches the same
string as that matched by the group named
"foo". Equivalent to \1, \2, etc.
except that the group is referred
to by name, not
number.

I hope that this Python-specific
extension won't conflict with any
future Perl extensions to the Perl regex
syntax. If you have plans to
use (?P, please let us know as soon as possible
so we can resolve the
conflict. Otherwise, it would be nice if
the (?P syntax could be
permanently reserved for Python-specific syntax
extensions. (Is
there some kind of registry of
extensions?)

to
which Larry Wall replied:

[...] There's no registry as of now--yours is the first request from

outside perl5-porters, so it's a pretty low-bandwidth activity.
(Sorry it
was even lower last week--I was off in New York at Internet

World.)

Anyway, as far as I'm concerned, you
may certainly have 'P' with my

blessing. (Obviously Perl doesn't
need the 'P' at this point. :-)
[...]

So I don't
know what the original choice of P was motivated by -- pattern? placeholder? penguins?
-- but you can understand why I've always associated it with Python. Which considering
that (1) I don't like regular expressions and avoid them wherever possible, and (2) this
thread happened fifteen years ago, is kind of odd.