Question

I have a Python Unicode string. I want to make sure it only contains letters from the Roman alphabet (A through Z), as well as letters commonly found in European alphabets, such as ß, ü, ø, é, à, and î. It should not contain characters from other alphabets (Chinese, Japanese, Korean, Arabic, Cyrillic, Hebrew, etc.). What’s the best way to go about doing this?

Currently I am using this bit of code, but I don’t know if it’s the best way:

def only_roman_chars(s):
    try:
        s.encode("iso-8859-1")
        return True
    except UnicodeDecodeError:
        return False

(I am using Python 2.5. I am also doing this in Django, so if the Django framework happens to have a way to handle such strings, I can use that functionality — I haven’t come across anything like that, however.)

Answer 1

import unicodedata as ud

latin_letters= {}

def is_latin(uchr):
    try: return latin_letters[uchr]
    except KeyError:
         return latin_letters.setdefault(uchr, 'LATIN' in ud.name(uchr))

def only_roman_chars(unistr):
    return all(is_latin(uchr)
           for uchr in unistr
           if uchr.isalpha()) # isalpha suggested by John Machin

>>> only_roman_chars(u"ελληνικά means greek")
False
>>> only_roman_chars(u"frappé")
True
>>> only_roman_chars(u"hôtel lœwe")
True
>>> only_roman_chars(u"123 ångstrom ð áß")
True
>>> only_roman_chars(u"russian: гага")
False