Simple Python function to validate IP address

 Here is a simple Python function that checks if a given string is a valid IP address:

import re 

def is_valid_ip(ip): 

    pattern = re.compile(r"^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$") 

    return pattern.match(ip) is not None

This function uses a regular expression to check if the input string is a valid IP address. The regular expression is compiled and stored in the variable 'pattern'. The match function is used to check if the string passed to the function matches the regular expression. If it does, the function returns True, otherwise, it returns False.

You can test the function by calling it and passing a string as an argument:

print(is_valid_ip("192.168.0.1")) # True 

print(is_valid_ip("256.256.256.256")) # False

Note that this function will only check if the string passed to it is a valid IP address in the format of 'xxx.xxx.xxx.xxx' where xxx is a number between 0 and 255.