Hi Gordon, You pose an interesting question that I don't think anyone has posed before. Having thought about it, I think that the keys in the group dict are similar to the names of variables or attributes, and I think treating them always as strings makes sense. For example, I might write a function that allows passing in a pattern and a search string, both either str or bytes, where the function would expect fixed keys in the group dict:
def extract_key_value(pattern, target): m = re.match(pattern, target) return m and m.groupdict['key'], m.groupdict['value'] There might be a problem with decoding the group name from the pattern, so sticking to ASCII group names would be wise. There's also the backwards compatibility concern: even if we did want to change this, would we want to break existing code (like the above) that might currently work? --Guido On Sun, Sep 25, 2016 at 5:25 PM, Gordon R. Burgess <gor...@parasamgate.com> wrote: > I've been lurking for a couple of months, working up the confidence to > ask the list about this behavior - I've searched through the PEPs but > couldn't find any specific reference to it. > > In a nutshell, in the Python 3.5 library re patterns and search buffers > both need to be either unicode or byte strings - but the keys in the > groupdict are always returned as str in either case. > > I don't know whether or not this is by design, but it would make more > sense to me if when searching a bytes object with a bytes pattern the > keys returned in the groupdict were bytes as well. > > I reworked the example a little just now so it would run it on 2.7 as > well; on 2.7 the keys in the dictionary correspond to the mode of the > pattern as expected (and bytes and unicode are interconverted silently) > - code and output are inline below. > > Thanks for your time, > > Gordon > > [Code] > > import sys > import re > from datetime import datetime > > data = (u"first string (unicode)", > b"second string (bytes)") > > pattern = [re.compile(u"(?P<ordinal>\\w+) .*\\((?P<type>\\w+)\\)"), > re.compile(b"(?P<ordinal>\\w+) .*\\((?P<type>\\w+)\\)")] > > print("*** re consistency check ***\nRun: %s\nVersion: Python %s\n" % > (datetime.now(), sys.version)) > for p in pattern: > for d in data: > try: > result = "groupdict: %s" % (p.match(d) and > p.match(d).groupdict()) > except Exception as e: > result = "error: %s" % e.args[0] > print("mode: %s\npattern: %s\ndata: %s\n%s\n" % > (type(p.pattern).__name__, p.pattern, d, result)) > > [Output] > > gordon@w540:~/workspace/regex_demo$ python3 regex_demo.py > *** re consistency check *** > Run: 2016-09-25 20:06:29.472332 > Version: Python 3.5.2+ (default, Sep 10 2016, 10:24:58) > [GCC 6.2.0 20160901] > > mode: str > pattern: (?P<ordinal>\w+) .*\((?P<type>\w+)\) > data: first string (unicode) > groupdict: {'ordinal': 'first', 'type': 'unicode'} > > mode: str > pattern: (?P<ordinal>\w+) .*\((?P<type>\w+)\) > data: b'second string (bytes)' > error: cannot use a string pattern on a bytes-like object > > mode: bytes > pattern: b'(?P<ordinal>\\w+) .*\\((?P<type>\\w+)\\)' > data: first string (unicode) > error: cannot use a bytes pattern on a string-like object > > mode: bytes > pattern: b'(?P<ordinal>\\w+) .*\\((?P<type>\\w+)\\)' > data: b'second string (bytes)' > groupdict: {'ordinal': b'second', 'type': b'bytes'} > > gordon@w540:~/workspace/regex_demo$ python regex_demo.py > *** re > consistency check *** > Run: 2016-09-25 20:06:23.375322 > Version: Python > 2.7.12+ (default, Sep 1 2016, 20:27:38) > [GCC 6.2.0 20160822] > > mode: unicode > pattern: (?P<ordinal>\w+) .*\((?P<type>\w+)\) > data: first string (unicode) > groupdict: {u'ordinal': u'first', u'type': u'unicode'} > > mode: unicode > pattern: (?P<ordinal>\w+) .*\((?P<type>\w+)\) > data: second string (bytes) > groupdict: {u'ordinal': 'second', u'type': 'bytes'} > > mode: str > pattern: (?P<ordinal>\w+) .*\((?P<type>\w+)\) > data: first string (unicode) > groupdict: {'ordinal': u'first', 'type': u'unicode'} > > mode: str > pattern: (?P<ordinal>\w+) .*\((?P<type>\w+)\) > data: second string (bytes) > groupdict: {'ordinal': 'second', 'type': 'bytes'} > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > https://mail.python.org/mailman/options/python-dev/guido%40python.org -- --Guido van Rossum (python.org/~guido) _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com