Why won't this user created function work?

[Evyeniarocks]

This is the code I wrote, but when it prints the message at the end, it prints the original input as if it had not gone through the string function. What's the problem?

message=str(raw_input("Enter the encoded string: "))
message=message.lower()

def strip(string):
    stripped_message=""
    for i in range(0,len(string)):
        character=ord(string[i:i+1])
        if character in range(97,123):
            stripped_message+=chr(character)
    return stripped_message


strip(message)
print message