On Feb 16, 2015, at 18:45, Ryan Gonzalez <rymg19@gmail.com> wrote:
It's usually in callbacks where you only care about a few arguments.
A perfect example is using Tk variable tracing in tkinter (for validation or post-change triggering on widgets). The signature of the trace callback is callback(name, index, mode). You almost never need the index, you rarely need the mode, so you write: def callback(self, name, _, mode): In fact, you usually don't need the mode either (in fact, you often don't even need the name), but you can't write this: def callback(self, name, _, _): So instead you usually write something like: def callback(self, name, *_): Personally, I find *_ ugly, so I use *dummy instead. But whatever. So anyway, what if you needed the index, but not the name or mode? You can't use *_ to get around that; you have to come up with two dummy names. That's a bit annoying. The question is, how often do you really need to ignore multiple parameters, but not all of them (or all of them from this point on)? I can't remember any callback API that I've used where that came up, but I can imagine someone else has one:
On Mon, Feb 16, 2015 at 8:41 PM, Steven D'Aprano <steve@pearwood.info> wrote:
On Mon, Feb 16, 2015 at 07:23:30PM -0600, Ryan Gonzalez wrote:
Often, underscores are used in function argument lists:
def f(_): pass
However, sometimes you want to ignore more than one argument, in which case this doesn't work:
Why are you ignoring *any* arguments?
-- Steve _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
-- Ryan If anybody ever asks me why I prefer C++ to C, my answer will be simple: "It's becauseslejfp23(@#Q*(E*EIdc-SEGFAULT. Wait, I don't think that was nul-terminated." Personal reality distortion fields are immune to contradictory evidence. - srean Check out my website: http://kirbyfan64.github.io/ _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/