Having just discovered that PEP 3131 [1] enables me to use greek letters to represent variables in equations, it was pointed out to me that it also allows visually confusable characters in identifiers [2]. When I previously read the PEP I thought that the normalisation process resolved these issues but now I see that the PEP leaves it as an open problem. I also previously thought that the PEP would be irrelevant if I was using ascii-only code but now I can see that if a GREEK CAPITAL LETTER ALPHA can sneak into my code (just like those pesky tab characters) I could still have a visually undetectable bug. An example to show how an issue could arise: """ #!/usr/bin/env python3 code = ''' {0} = 123 {1} = 456 print('"{0}" == "{1}":', "{0}" == "{1}") print('{0} == {1}:', {0} == {1}) ''' def test_identifier(identifier1, identifier2): exec(code.format(identifier1, identifier2)) test_identifier('\u212b', '\u00c5') # Different Angstrom code points test_identifier('A', '\u0391') # LATIN/GREEK CAPITAL A/ALPHA """ When I run this I get: $ ./test.py "Å" == "Å": False Å == Å: True "A" == "Α": False A == Α: False Is the proposal mentioned in the PEP (to use something based on Unicode Technical Standard #39 [3]) something that might be implemented at any point? Oscar References: [1] http://www.python.org/dev/peps/pep-3131/#open-issues [2] http://article.gmane.org/gmane.comp.python.tutor/78116 [3] http://unicode.org/reports/tr39/#Confusable_Detection