On Sun, Nov 15, 2020 at 03:18:29PM +0300, Paul Sokolovsky wrote: > > > amount of work to implement pattern matching is certainly an order > > > of magnitude larger than to introduce constants [...]
[Steve] > > Here's a toy proposal, > [] > > The baseline of my version is much simpler: > > # This makes "const" a kind of hard keyword for this module > from __future__ import const > > FOO: const = 1 # obviously, this is constant > Foo_Bar: const = 2 # this is too > foo: const = 3 # and like it or not, but this is constant either > > "const" annotation is recognized by compiler (scope resolving > component, aka symtable builder to be exact) as a property orthogonal to > localness/globalness. Literally, "symtable" module > (https://docs.python.org/3/library/symtable.html#symtable.Symbol) will > grow Symbol.is_const() method. Oh, well, if all it takes is to add a new keyword, then constants are easy! No need to worry about how constantness affects name resolution, or how the syntax interacts with type-hints: spam: const: Widget = build_widget(*args) # Maybe this is better? # let spam: Widget = build_widget(*args) or how "constant" interacts with mutability: spam: const = [] spam.append(99) # Allowed? spam.extend(items) spam.sort() or for that matter, whether or not constants are actually constant. spam: const = 1 spam = 2 If constants aren't actually constant, but just a tag on symbols, then you would be right, it probably would be trivially easy to add "constants" to Python. But I think most people agree making them behave as constants is a pretty important feature. *The* most critical feature of all, really. Given a declared constant: # Module a.py x: const = None how do you prevent not just code in module `a` from rebinding the value: x = 1 globals()['x'] = 2 exec('x = 3', globals()) but other modules as well: # Module b.py import a a.x = 'spam' vars(a)['x'] = 'spam' exec('x = 3', vars(a)) -- Steve _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/MVDPBRBONUQXJK2RW5VX24YCGD4NX3EM/ Code of Conduct: http://python.org/psf/codeofconduct/
