diff options
Diffstat (limited to 'Doc/library/re.rst')
| -rw-r--r-- | Doc/library/re.rst | 40 |
1 files changed, 26 insertions, 14 deletions
diff --git a/Doc/library/re.rst b/Doc/library/re.rst index b0cb870..1421f35 100644 --- a/Doc/library/re.rst +++ b/Doc/library/re.rst @@ -242,21 +242,32 @@ The special characters are: ``(?P<name>...)`` Similar to regular parentheses, but the substring matched by the group is - accessible within the rest of the regular expression via the symbolic group - name *name*. Group names must be valid Python identifiers, and each group - name must be defined only once within a regular expression. A symbolic group - is also a numbered group, just as if the group were not named. So the group - named ``id`` in the example below can also be referenced as the numbered group - ``1``. - - For example, if the pattern is ``(?P<id>[a-zA-Z_]\w*)``, the group can be - referenced by its name in arguments to methods of match objects, such as - ``m.group('id')`` or ``m.end('id')``, and also by name in the regular - expression itself (using ``(?P=id)``) and replacement text given to - ``.sub()`` (using ``\g<id>``). + accessible via the symbolic group name *name*. Group names must be valid + Python identifiers, and each group name must be defined only once within a + regular expression. A symbolic group is also a numbered group, just as if + the group were not named. + + Named groups can be referenced in three contexts. If the pattern is + ``(?P<quote>['"]).*?(?P=quote)`` (i.e. matching a string quoted with either + single or double quotes): + + +---------------------------------------+----------------------------------+ + | Context of reference to group "quote" | Ways to reference it | + +=======================================+==================================+ + | in the same pattern itself | * ``(?P=quote)`` (as shown) | + | | * ``\1`` | + +---------------------------------------+----------------------------------+ + | when processing match object ``m`` | * ``m.group('quote')`` | + | | * ``m.end('quote')`` (etc.) | + +---------------------------------------+----------------------------------+ + | in a string passed to the ``repl`` | * ``\g<quote>`` | + | argument of ``re.sub()`` | * ``\g<1>`` | + | | * ``\1`` | + +---------------------------------------+----------------------------------+ ``(?P=name)`` - Matches whatever text was matched by the earlier group named *name*. + A backreference to a named group; it matches whatever text was matched by the + earlier group named *name*. ``(?#...)`` A comment; the contents of the parentheses are simply ignored. @@ -667,7 +678,8 @@ form. when not adjacent to a previous match, so ``sub('x*', '-', 'abc')`` returns ``'-a-b-c-'``. - In addition to character escapes and backreferences as described above, + In string-type *repl* arguments, in addition to the character escapes and + backreferences described above, ``\g<name>`` will use the substring matched by the group named ``name``, as defined by the ``(?P<name>...)`` syntax. ``\g<number>`` uses the corresponding group number; ``\g<2>`` is therefore equivalent to ``\2``, but isn't ambiguous |