Re: correct way to catch exception with Python 'with' statement

On 2016-12-02, Marko Rauhamaa wrote: > Grant Edwards : >> In general CISC processors like x86, AMD64, 68K have read-modify-write >> instructions that allow you to increment a memory location or >> set/clear a bit in memory with a single instruction: >>

Re: correct way to catch exception with Python 'with' statement

Grant Edwards : > In general CISC processors like x86, AMD64, 68K have read-modify-write > instructions that allow you to increment a memory location or > set/clear a bit in memory with a single instruction: > > INC.W [R0]# increment memory word whose addr is in

Re: correct way to catch exception with Python 'with' statement

On 12/01/2016 08:39 PM, Ned Batchelder wrote: > On Thursday, December 1, 2016 at 7:26:18 PM UTC-5, DFS wrote: >> How is it possible that the 'if' portion runs, then 44/100,000ths of a >> second later my process yields to another process which deletes the >> file, then my process continues. > >

Re: correct way to catch exception with Python 'with' statement

On 2016-12-02, Steve D'Aprano wrote: > I'm not an expert on the low-level hardware details, so I welcome > correction, but I think that you can probably expect that the OS can > interrupt code execution between any two CPU instructions. Yep, mostly. Some CPUs have

Re: correct way to catch exception with Python 'with' statement

On Fri, 2 Dec 2016 11:26 am, DFS wrote: >> For most programs, yes, it probably will never be a problem to check >> for existence, and then assume that the file still exists.  But put that >> code on a server, and run it a couple of million times, with dozens of >> other processes also

Re: correct way to catch exception with Python 'with' statement

On Fri, 2 Dec 2016 11:26 am, DFS wrote: > On 12/01/2016 06:48 PM, Ned Batchelder wrote: >> On Thursday, December 1, 2016 at 2:31:11 PM UTC-5, DFS wrote: >>> After a simple test below, I submit that the above scenario would never >>> occur. Ever. The time gap between checking for the file's

Re: correct way to catch exception with Python 'with' statement

On Thursday, December 1, 2016 at 7:26:18 PM UTC-5, DFS wrote: > On 12/01/2016 06:48 PM, Ned Batchelder wrote: > > On Thursday, December 1, 2016 at 2:31:11 PM UTC-5, DFS wrote: > >> After a simple test below, I submit that the above scenario would never > >> occur. Ever. The time gap between

Re: correct way to catch exception with Python 'with' statement

On Thursday, December 1, 2016 at 2:31:11 PM UTC-5, DFS wrote: > After a simple test below, I submit that the above scenario would never > occur. Ever. The time gap between checking for the file's existence > and then trying to open it is far too short for another process to sneak > in and

Re: correct way to catch exception with Python 'with' statement

On Wed, 30 Nov 2016 05:35 pm, DFS wrote: > On 11/29/2016 10:20 PM, Steven D'Aprano wrote: >> On Wednesday 30 November 2016 10:59, woo...@gmail.com wrote: >> >>> If you want to do something only if the file exists (or does not), use >>> os.path.isfile(filename) >> >> No, don't do that. Just

Re: correct way to catch exception with Python 'with' statement

Marko Rauhamaa : > Peter Otten <__pete...@web.de>: > >> Marko Rauhamaa wrote: >>>try: >>>f = open("xyz") >>>except FileNotFoundError: >>>...[B]... >>>try: >>>...[A]... >>>finally: >>>f.close() >> >> What's the problem with spelling

Re: correct way to catch exception with Python 'with' statement

On Wednesday 30 November 2016 10:59, woo...@gmail.com wrote: > If you want to do something only if the file exists (or does not), use > os.path.isfile(filename) No, don't do that. Just because the file exists, doesn't mean that you have permission to read or write to it. Worse, the code is

Re: correct way to catch exception with Python 'with' statement

On Tue, 29 Nov 2016 at 23:59 wrote: > If you want to do something only if the file exists (or does not), use > os.path.isfile(filename) > This opens you up to a potential race condition (and has potential security implications, depending on the application), as you're using

Re: correct way to catch exception with Python 'with' statement

If you want to do something only if the file exists (or does not), use os.path.isfile(filename) -- https://mail.python.org/mailman/listinfo/python-list

Re: correct way to catch exception with Python 'with' statement

Peter Otten <__pete...@web.de>: > Marko Rauhamaa wrote: > >> However, I think the real answer is that you shouldn't mix the "with" >> construct with exception handling. Instead you should write: >> >>try: >>f = open("xyz") >>except FileNotFoundError: >>...[B]... >>

Re: correct way to catch exception with Python 'with' statement

Marko Rauhamaa wrote: > However, I think the real answer is that you shouldn't mix the "with" > construct with exception handling. Instead you should write: > >try: >f = open("xyz") >except FileNotFoundError: >...[B]... >try: >...[A]... >finally: >

Re: correct way to catch exception with Python 'with' statement

Steven D'Aprano : > There is no need to catch the exception if you're not going to do > anything with it. Correct. However, the question of the subject line is still a good one. See: try: with open("xyz") as f: ...[A]... except

Re: correct way to catch exception with Python 'with' statement

Thanks Steve I got what you were trying to explain , nice learning from this conversation , what I was really doing wrong I had broken down my huge code into a simple program and had missed out returning False. On Tue, Nov 29, 2016 at 11:01 AM, Steven D'Aprano <

Re: correct way to catch exception with Python 'with' statement

On Tuesday 29 November 2016 02:18, Ganesh Pal wrote: > On Mon, Nov 28, 2016 at 1:16 PM, Steven D'Aprano < > steve+comp.lang.pyt...@pearwood.info> wrote: > >> >> >> There is no need to return True. The function either succeeds, or it >> raises an >> exception, so there is no need to return any

correct way to catch exception with Python 'with' statement

Dear Python friends, Any suggestion on how to add exception and make the below program look better , I am using Python 2.7 and Linux def create_files_append(): """ """ try:

Re: correct way to catch exception with Python 'with' statement

Ganesh Pal wrote: > I am using Python 2.7 and Linux As a rule of thumb¹, use at least Python 3.3 for new programs. > What will be the best way to catch the exception in the above program ? > Can we replace both the with statement in the above program with > something like below > > try: >

Re: correct way to catch exception with Python 'with' statement

On 11/28/2016 08:18 AM, Ganesh Pal wrote: > On Mon, Nov 28, 2016 at 1:16 PM, Steven D'Aprano < > steve+comp.lang.pyt...@pearwood.info> wrote: > >> >> >> There is no need to return True. The function either succeeds, or it >> raises an >> exception, so there is no need to return any value at all.

Re: correct way to catch exception with Python 'with' statement

On Mon, Nov 28, 2016 at 1:16 PM, Steven D'Aprano < steve+comp.lang.pyt...@pearwood.info> wrote: > > > There is no need to return True. The function either succeeds, or it > raises an > exception, so there is no need to return any value at all. > > I returned True here ,because based on the

Re: correct way to catch exception with Python 'with' statement

On Monday 28 November 2016 17:09, Ganesh Pal wrote: > Dear Python friends, > > Any suggestion on how to add exception and make the below program look > better , I am using Python 2.7 and Linux > > >

correct way to catch exception with Python 'with' statement

Dear Python friends, Any suggestion on how to add exception and make the below program look better , I am using Python 2.7 and Linux def create_files_append(): """ """ try: