On 16/07/2020 18:13, MRAB wrote:
On 2020-07-16 17:37, Steve Holden wrote:
While I understand the point of view that says that match ... :
should encapsulate a sequence of indented suites, it seems to me that
match/case/case/.../else has a natural affinity with
try/except/except/.../finally/else, and nobody seems to think that
the excepts should be indented. Or the finally. And naturally the
match/else case are at the same indentation level, just as for/else,
while/else and try/finally. So why, exactly, should case be indented?
My apologies for being a Bear of Very Little Brain.
[snip]
For all other statement structures (if, while, try, etc.), the first
line ends with a colon and the second line is indented (and is a
statement). Therefore the cases should be indented.
However, for all other statement structures (if, while, try, etc.),
the other parts of the structure itself (elif, else, except, etc.)
aren't indented. Therefore the cases shouldn't be indented.
Either way, it's inelegant.
Absolutely true. However:
I think that equal indentation suggests suites of equal status.
Increased indentation suggests suites are subordinate to a previous suite.
Consider these examples:
(1) if..elif...else: Suites are definitely co-equal (they are
alternatives, only one of which is chosen). So if/elif/else have equal
indentation.
(2) for...else or while...else: It's arguable IMO (YMMV); Python has
chosen to indent them equally. I don't think it would have been
outrageous to indent the 'else:'; one reason not to is that the 'else'
might not stand out (it would typically be indented equally with the
preceding line of code), unless it was allowed/forced to be indented
*less than* 'for'.
(3) try...except...else: IMO also arguable (at most one of 'except' and
'else' can be executed).
(4) try...finally: The suites have equal status (both are always
executed), so they have equal indentation.
Now to me, 'case' clauses are *subordinate* to 'match'. After all, the
value after 'match' applies to all the following 'case's. So I would
argue in favour of indenting 'case' statements. This would make them
stand out *more* (making a virtue out of 'match' *not* being followed by
an indented suite). A Good Thing. One of the purposes of indentation
is to make program structure clearly visible, which IMO this would do.
Or from a slightly different point of view: "match...case...case..." is
a single construct, a self-contained program component. Indenting the
'case's would stop them from distracting visually from other suites that
are indented the same as 'match'. (I.e. other program components of
equal status.)
(If 'else' were allowed after 'match', I would argue that it should also
be indented, for the same reasons, and because it is logically a case,
albeit a special one.)
Rob Cliffe
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