What am I doing wrong/what can I do?

import sys
import string

def remove(file):
    punctuation = string.punctuation
    for ch in file:
        if len(ch) > 1:
            print('error - ch is larger than 1 --| {0} |--'.format(ch))
        if ch in punctuation:
            ch = ' '
            return ch
        else:
            return ch

ref = (open("ref.txt","r"))
test_file = (open("test.txt", "r"))

dictionary = ref.read().split()
file = test_file.read().lower()
file = remove(file)
print(file)

This is in Python 3.1.2