On 15/03/2016 00:12, Chris Angelico wrote:
On Tue, Mar 15, 2016 at 10:56 AM, BartC <b...@freeuk.com> wrote:
switch c
when 'A'..'Z','a'..'z','_' then
++name
Anything so terrible about that that Python needs to keep well clear of or
that you think its users should be deprived of?
Yes: the complete lack of colons at the ends of lines that introduce
suites. This is utterly unacceptable in Python!
Seriously though - the one thing that I'm very concerned about here is
your brackets one.
Yeah, I'm not sure about that either. I'd already written:
when '(', ')', ....
when I thought having a string constant here would be neat, and
implemented that just before posting.
In Python, there's no reason to restrict 'switch'
to integers, so I would expect its semantics to be based on either
equality comparisons or inequality comparisons
I use two forms of switch: one for integers only (very fast), and the
other for any other values, which does tests in sequence.
(possibly with a
requirement that all values be hashable); you could have something
like "when in <string>" but a simple "when <string>" would look to me
like it's testing for that entire string. (Don't forget that, in
Python, there's no difference between 'single quoted strings' and
"double quoted strings", as there is in C-like languages.)
Although... come to think of it, you could actually define it the
other way around: the 'when' statement checks if the current switch
object is contained within any of its arguments. Coupled with a
range-like object with its own literal syntax, that would pretty much
give you what you're looking at there. However, you'd need to have an
awkward notation for the cases where you _are_ looking for equality:
switch c:
when 'A'..'Z', 'a'..'z', ['_']:
++name
Or, in a long tree:
switch c:
when [1]:
...
when [2]:
...
when [3]:
...
Which could work. It'd be well-defined, and not unreasonable. It
would, however, be entirely predicated on a "comparison range" object
with a literal syntax:
class Range:
def __init__(self, start, stop):
self.start = start
self.stop = stop
def __contains__(self, obj):
return self.start <= obj <= self.stop
def __repr__(self):
return "%r..%r" % (self.start, self.stop)
But that's not overly hard either.
The tests I do for the more general switch are either equality, or 'in'
for certain combinations of types (mainly testing integers for
membership of ranges and sets. Sets are Pascal-style bit-sets).
I've also looked at the problem of when the choice might be ambiguous:
case x # general 'switch'
when y then
...
What happens when y is a list; should it do x==y or x in y? (Or both?)
I haven't solved that yet but it's never come up. When x is anything
other than an int, you invariably want an equality test.
--
Bartc
--
https://mail.python.org/mailman/listinfo/python-list
