try:
    name = raw_input("Представьтесь: ").strip()
    if not re.match(r'^[a-zA-Z0-9]+$', name):
        pass
except ValueError:
    print "Разрешены только буквы латинского алфавита и цифры"
c.execute("SELECT COUNT(login) FROM user WHERE user.login=?", (name,))

вот такая ошибка:
sqlite3.ProgrammingError: You must not use 8-bit bytestrings unless you use a text_factory that can interpret 8-bit bytestrings (like text_factory = str). It is highly recommended that you instead just switch your application to Unicode strings.