Re: Best use of "open" context manager

On 07/07/2024 02:08, Cameron Simpson wrote:

On 06Jul2024 11:49, Rob Cliffe <rob.cliffe@btinternet.com> wrote:

try:
    f = open(FileName) as f:
    FileLines = f.readlines()
except FileNotFoundError:
    print(f"File {FileName} not found")
    sys.exit()
# I forgot to put "f.close()" here -:)
for ln in File Lines:
        print("I do a lot of processing here")
        # Many lines of code here .....

>
What about this:
>
    try:
        f = open(FileName) as f:
    except FileNotFoundError:
        print(f"File {FileName} not found")
        sys.exit()
    with f:
        ... process the lines here ...
>
Remember, the `open()` call returns a file object _which can be used as a context manager_. It is separate from the `with` itself.

Did you test this?
     f = open(FileName) as f:
is not legal syntax.
If you omit the "as f:"
it's legal, but doesn't work (trying to access the file after "with f" raises the same
     ValueError: I/O operation on closed file.
I'm using Python 3.11.5.
Best wishes
Rob Cliffe