Why not allow empty code blocks?

[BartC]

On 23/07/2016 16:55, Steven D'Aprano wrote:
> On Sun, 24 Jul 2016 12:06 am, BartC wrote:
>
>> pass can only do so much. If doesn't help here:
>>
>>   for x in sequence:
>>       print("Something")
>>   print("Something else")
>>
>> Was the second print meant to be indented as well or not?
>
> True. But once you start wondering about code the programmer *hasn't*
> written, you could drive yourself crazy:
>
>     ...but what if the second print is supposed to follow
>     an "if" clause, which has been left out...?

I didn't want to get into this subject again, but Python's indentation 
scheme is fragile.

Given an otherwise correctly typed program that compiles with no errors, 
then it is very easy (if Backspace or Delete is inadvertently pressed 
for example), for an indent to disappear without your noticing, but a 
program still compiles. And still runs without execution errors. But 
might now be subtly wrong.

Deleting any other character than a leading space or tab I think is more 
likely to result in an error that would be noticed, generate a compile 
error, or execute error ('variable not initialised'), or that goes wrong 
more obviously.

>> Perhaps rather than 'pass', the language ought to have provided an
>> optional 'end' keyword to mark the end of a block. Then there would be
>> less speculation about what was meant:
>
> It can't be optional. If it were optional, we'd be no better off:
>
>     for x in sequence:
>     print(x)

But that's a choice. Being optional, it means someone /can/ make use of 
it...

> The "end" is missing, but is it missing from the end of the empty block, or
> the end of the non-empty block?
>
>     for x in sequence:
>     end
>     print(x)
>
>     for x in sequence:
>     print(x)
>     end

...then it might look like the first example above. The second would be 
an error.

>
> In any case, using "end" instead of "pass" is a poor tradeoff. Instead of
> needing to use "pass" (say) one time in a thousand when it is needed, you
> would need to use "end" 999 times in a thousand when it *isn't* needed.

Yes, well, some of us wouldn't mind! But my suggestion is simply that 
you can write:

      for x in sequence:
      end

instead of:

      for x in sequence:
          pass

The first now allows statements to be added or removed from the body of 
the loop without needing to change the 'end'; it wouldn't look out of 
place as a trailing 'pass' would.

But thinking about it some more, it wouldn't work. All the blocks that 
don't now use 'end' would look odd. I think it would either have to be 
all or nothing. I guess nothing.

-- 
Bartc