.Python.

Can someone help me with my code on the characters that it validates? Acceptable input is zero or more characters from these characters only {a, b, +, *, (, )}. and make the program show what characters are invalid like the sample.

import re valid_chars = "[a\b\|\*\(\)]"

print("Regular expression validator over the alphabet {a,b, |, *, (, )}") # intructions for the user

while True: expression = input("Enter regular expression: ") if expression == "": break if re.fullmatch(valid_chars, expression): print("VALID:", expression) else: invalid_chars = "".join(re.findall("[^c-zA-Z\0-9\!\@\#\$\%\&]", expression)) <- I do not know how to put everything that is invalid in here print("INVALID:", expression)

for char in invalid_chars: print("^", end="") print()

print("Program terminated.")

here is the sample input and output Regular expression validator over the alphabet {a, b, +, *, (, )} Enter regular expression: ab VALID: ab Enter regular expression: ab ( ba)* VALID: ab(ba)* Enter regular expression: ab ( ba)*X+ba ( bb INVALID: ab(ba)*X+ba(bb ^^ Enter regular expression: ) & 0 # $ b ( - b a)*X | ba ( bb INVALID: )&a#$b(-ba)*X | ba(bb ^ ^^ ^ ^ Program terminated.