[Python-Dev] os.path.walk() lacks 'depth first' option

[Michael Hudson]

Tim Peters <tim.one@comcast.net> writes:

> [Jeremy Fincher]
>> This code brought up an interesting question to me: if sets have
>> a .discard method that removes an element without raising KeyError
>> if the element isn't in the set, should lists perhaps have that same
>> method?
>
> I don't think list.remove(x) is used enough to care, when the presence of x
> in the list is unknown.

I've wished for this, more than once, in the past.  I can't quite
remember why, I have to admit.

while x in seq:
    seq.remove(x)

is vulgar, on at least two levels.

For all that, I'm not sure this is worth the pain.

>> On another related front, sets (in my Python 2.3a2) raise KeyError on a
>> .remove(elt) when elt isn't in the set.  Since sets aren't mappings,
>> should that be a ValueError (like list raises) instead?
>
> Since sets aren't sequences either, why should sets raise the same exception
> lists raise?  It's up to the type to use whichever fool exceptions it
> chooses.  This doesn't always make life easy for users, alas -- there's not
> much consistency in exception behavior across packages.  In this case, a
> user would be wise to avoid expecting IndexError or KeyError, and catch
> their common base class (LookupError) instead.  The distinction between
> IndexError and KeyError isn't really useful (IMO; LookupError was injected
> as a base class recently in Python's life).

Without me noticing, too!  Well, I knew there was a lookup error that
you get when failing to find a codec, but I didn't know IndexError and
KeyError derived from it...

Also note that Jeremy was suggesting *ValueError*, not
IndexError... that any kind of index-or-key-ing is going on is trivia
of the implementation, surely?

Cheers,
M.

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