PS: I really tried to find a way to use := in this example so I could
put the assignment inside the 'if' statement, but as I think Tim Peters
pointed out, without C's comma operator, you can't.
Conceivably cut_prefix could return None if not found. Then you could write something like:
if (stripped := cut_prefix(line, "INFO>")) is not None:
print(f"control line {stripped!r}")
else:
print(f"data line {line!r}")
You could even drop "is not None" in many circumstances, if you know the cut string will be non-empty. That's actually pretty readable:
if stripped := cut_prefix(line, "INFO>"):
print(f"control line {stripped!r}")
else:
print(f"data line {line!r}")