[Python-ideas] except expression

[MRAB]

On 2014-02-15 19:57, Steven D'Aprano wrote:
> On Sat, Feb 15, 2014 at 08:24:09PM +0100, Philipp A. wrote:
>> hmm i still don’t like the colon. everywhere else in python, it means “new
>> block follows”
>
> That is incorrect. Did you read my full post? I specifically mentioned
> both dicts and lambda, both of which use colons in expressions, and
> don't start a new block.
>
It's also used in slices.

>
>> and i’m sure nobody here wants to allow the following?
>>
>> value = hovercraft() except EelsException:
>>    remove_eels()
>>    no_eels  #this is assigned to “value” if we have too many eels
>
> That's not the suggested syntax.
>
> To start with, if you want to spread the expression over multiple lines,
> you need either line continuation backslashes, or round brackets:
>
> value = hovercraft() (except EelsException:
>      remove_eels()
>      )
>
>
> Secondly, you then place an unexpected "no_eels" statement after the
> expression. That will be a syntax error.
>
>
>> i like it in coffeescript and scala, but it’s not used in python, so we
>> shouldn’t introduce it.
>
> What is used in coffeescript and scala?
>
>
>> neither should we introduce a colon that *can’t* be followed by a block.
>
> Dicts, lambda.
>
>
>> if we wanted the colon in any case, we’d need to do:
>>
>> winner = germans_win() except EurekaException: return greeks
>
> Certainly not. Do we write this?
>
> mydict = {1: return 'a', 2: return 'b'}
>
>
>> value = hovercraft() except EelsException:
>>    remove_eels()
>>    return no_eels
>
> This is not the suggested syntax. I suggest you read my post again, and
> notice that this is an *expression*. That is the whole point of the
> thread! If you want a block made up of multiple statements, use a
> try...except statement.
>
>
>> but i’m still partial to stomach_content = eat() except ThinMintError pass
>> explode()
>
> "pass" is a placeholder null statement, it has no relevance to
> try...except. You might just as well sensibly say
>
> stomach_content = eat() except ThinMintError import explode()
> stomach_content = eat() except ThinMintError del explode()
> stomach_content = eat() except ThinMintError class explode()
> stomach_content = eat() except ThinMintError def explode()
> stomach_content = eat() except ThinMintError pass explode()
>
> In all of these cases, I have picked a random keyword and just tossed it
> into the expression. None of them make any sense.
>