How can I check if a string contains ANY letters from the alphabet?

Regex should be a fast approach:

re.search('[a-zA-Z]', the_string)

How about:

>>> string_1 = "(555).555-5555"
>>> string_2 = "(555) 555 - 5555 ext. 5555"
>>> any(c.isalpha() for c in string_1)
False
>>> any(c.isalpha() for c in string_2)
True