On Thu, May 28, 2020 at 07:00:51PM +1200, Greg Ewing wrote: > On 28/05/20 12:38 pm, Rob Cliffe wrote: > >why not go further (as the OP suggested as far as I recall) > >and allow the more concise > > > > def order(eggs = 4, spam ?= Spam()): > > etc. > > That clutters up the header with things that are not part of > the function's signature. All the caller needs to know is that > the spam argument is optional.
I don't think you thought that through all the way. "All I need to know is that the mode argument to `open()` is optional, I don't need to know whether it defaults to read or write..." I don't think so. > The fact that a new Spam object > is created on each call if he doesn't supply one is an > implementation detail. Being an implementation detail implies that the functional behaviour will be identical either way, but that's incorrect under at least four circumstances: - Spam objects are mutable, e.g. lists, dicts, set; - calling Spam has side-effects; - calling Spam is particularly costly; - or if the result of calling Spam depends on the current state of the runtime environment, e.g. anything time dependent, anything to do with the state of the file system or a database, etc. The default value used by a parameter is certainly important, and one of the most common reasons I call `help(func)` is to see what the default values are. They should be in the signature, and it is an annoyance when all the signature shows is that it is None, and then I have to trawl through screenfuls of docs, or search the web, to find out what the actual default is. -- Steven _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/IL3K5G2K4Y752HQKA26EEZCIGNOT56P4/ Code of Conduct: http://python.org/psf/codeofconduct/
