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/archive%40mail-archive.com