It is possible to match a range of characters instead of just one. This can add some flexibility to the pattern:

• [A-Z] matches all capital letters
• [a-z] matches all lowercase letters
• [0-9] matches all digits

....
lower_case_letter = re.compile("[a-z]")
if lower_case_letter.search("a"):
    print("'a' is a match")
if lower_case_letter.search("B"):
    print("'B' is a match")
if lower_case_letter.search("123 A B 2"):
    print("'123 A B 2' is a match")

digit = re.compile("[0-9]")
if digit.search("1"):
    print("'a' is a match")
if digit.search("342"):
    print("'a' is a match")
if digit.search("asdf abcd"):
    print("'a' is a match")