Como ficaria o caso de textos com letras acentuadas?
LETRAS = 'aáàbcdeífghiéjklmnoópqrstuúvwxyzAÀÁBCDEÉFGHIÍJKLMNOÓPQRSTUÚVWXYZ'
Python 3.4.3 (default, Mar 26 2015, 22:03:40) [GCC 4.9.2] on linux Type "help", "copyright", "credits" or "license" for more information. >>> str = "a" >>> str.isalpha() True >>> "a".isalpha() True >>> "e".isalpha() True >>> str = "1" >>> str.isalpha() False >>> s = "*" >>> s.isalpha() False >>> s = "oi" >>> s.isalpha() True >>> s = "oi1" >>> s.isalpha() False >>> "é".isalpha() True >>> "à".isalpha() True >>> "também".isalpha() True >>> "também,".isalpha() False >>> help(str.isalpha) Help on built-in function isalpha: isalpha(...) method of builtins.str instance S.isalpha() -> bool Return True if all characters in S are alphabetic and there is at least one character in S, False otherwise. >>>