Re: Best use of "open" context manager (Posting On Python-List Prohibited)

On 6 Jul 2024 11:46:33 GMT, Stefan Ram wrote:

but this of course does not work because by the time we get to "for ln
in f:" the file has been closed so we get ValueError: I/O operation on
closed file

 
try:
    f = open( FileName )
except FileNotFoundError:
    print( f"File {FileName} not found" )
    sys.exit()
else:
    with f:
        # put this into a separate function if it gets too long here.
        for ln in f:
            print( "I do a lot of processing here" )
            # Many lines of code here .....

    f = open(filename, "rt")
    for ln in f :
        ... do your processing ...

1) Let the error exception be reported directly, whether it’s “file not
found”, or “permission error”, or some other reason; why bother to handle
it when you don’t even know what to do anyway?
2) Notice that a file open for reading automatically gets closed when it
goes out of scope (feature of CPython and all the other good
implementations).