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Xref: csiph.com comp.lang.python:34498

On 2012-12-08 07:17, Chris Angelico wrote:
> On Sat, Dec 8, 2012 at 6:01 PM, Terry Reedy <tjreedy@udel.edu> wrote:
>> Unfortunately, catching exceptions may be and often is as slow as the
>> redundant check and even multiple redundant checks.
>
> It depends on how often you're going to catch and how often just flow
> through. In Python, as in most other modern languages, exceptions only
> cost you when they get thrown. The extra check, though, costs you in
> the normal case.
>
That's where the .get method comes in handy:

MISSING = object()
...
value = my_dict.get(key, MISSING)
if value is not MISSING:
    ...

It could be faster if the dict often doesn't contain the key.