print( * open('script py'read('import sys\nprint(sys path)\nx \nprint( * )\nrecall from that open file objects have method called readlinewhich reads one line of text from file at time--each time we call the readline methodwe advance to the next line at the end of the filean empty string is returnedwhich we can detect to break out of the loopf open('script py' readline('import sys\nf readline('print(sys path)\nf readline(' \nf readline('print( * )\nf readline('read four-line script file in this directory readline loads one line on each call last lines may have \ or not returns empty string at end-of-file howeverfiles also have method named __next__ in (and next in xthat has nearly identical effect--it returns the next line from file each time it is called the only noticeable difference is that __next__ raises built-in stopiteration exception at end-of-file instead of returning an empty stringf open('script py'__next__ loads one line on each call too __next__(but raises an exception at end-of-file 'import sys\nf __next__(use next(in xor next(fin or 'print(sys path)\nf __next__(' \nf __next__('print( * )\nf __next__(traceback (most recent call last)file ""line in stopiteration this interface is most of what we call the iteration protocol in python any object with __next__ method to advance to next resultwhich raises stopiteration at the end of the series of resultsis considered an iterator in python any such object may also be stepped through with for loop or other iteration toolbecause all iteration tools normally work internally by calling __next__ on each iteration and catching the stopit eration exception to determine when to exit as we'll see in momentfor some objects the full protocol includes an additional first step to call iterbut this isn' required for files iterationsa first look