This arose from this SO question: https://stackoverflow.com/questions/52446415/line-in-iterfp-readline-rather-than-line-in-fp 

The example given in the docs:

with open('mydata.txt') as fp:
    for line in iter(fp.readline, ''):
        process_line(line)

Is exactly equivalent to the following because an empty string is only returned by readline at the EOF:

with open('mydata.txt') as fp:
    for line in fp:
        process_line(line)

The empty string '' sentinel value could be changed to another value to provide a possibly more meaningful example where the 2nd code snippet would not always produce the same result?