+def ip_v4_sort_key(txt: str) -> str:
+ """Turn an IPv4 address into a tuple for sorting purposes.
+
+ >>> ip_v4_sort_key('10.0.0.18')
+ (10, 0, 0, 18)
+
+ """
+ if not is_ip_v4(txt):
+ print(f"not IP: {txt}")
+ return None
+ return tuple([int(x) for x in txt.split('.')])
+
+