explicitly forbidden as well as numeric group references.

now is non-modifiable mapping.

and ASCII letter now raise a deprecation warning and will be forbidden in
Python 3.6.

conditional group references are used in lookbehind assertions in regular
expressions.

work in lookbehind assertions in regular expressions.

raises a warning.  Patterns that can only match empty strings are now
rejected.

re.ASCII. It was newer worked.

different lowercase are now matched in case-insensitive regular expressions.

work in lookbehind assertions in regular expressions.

Added new opcode RANGE_IGNORE.

locale-dependent regular expressions taking into account the locale.

and re.subn().

limited by 100.

regular expressions.

module.

with ignore case.  Original patch by Matthew Barnett.

as documented.  The pattern and source keyword parameters are left as
deprecated aliases.

Issue #20426: When passing the re.DEBUG flag, re.compile() displays the debug output every time it is called, regardless of the compilation cache.

which anchor the pattern at both ends of the string to match.

Original patch by Matthew Barnett.

Based on patch by Hugo Lopes Tavares.

and groups() methods of match object now always return a string or a bytes
object.

pattern at both ends of the string to match.

Patch by Matthew Barnett.
Closes #16203.