+100 I like this idea of giving `slice` a metaclass that defines a `.__getitem__()` allowing us to construct slices on the slice type itself.
FWIW, this is exactly what pandas.IndexSlice does. E.g., from http://pandas.pydata.org/pandas-docs/stable/advanced.html: In [51]: dfmi.loc[(slice('A1','A3'),slice(None), ['C1','C3']),:] In [52]: idx = pd.IndexSlice In [53]: dfmi.loc[idx[:,:,['C1','C3']],idx[:,'foo']] This is one of those nifty things that's buried in Pandas but not well documented. I'd rather spell the above simply as: dfmi.loc[slice[:,:,['C1','C3']], slice[:,'foo']] I like the change proposed to `str(slice(10))` also... and it would be way better if `slice[:10]` were actual "syntax." In fact, in that case it could even be the repr(). Note: Notwithstanding my scare quotes, Steven isn't actually asking for new syntax. "slice" is already a name, and names can already be followed by square brackets. He's just asking for a new method on a metaclass. On Sat, Nov 12, 2016 at 1:26 AM, Steven D'Aprano <st...@pearwood.info> wrote: > On Thu, Oct 06, 2016 at 04:19:17PM -0700, Neil Girdhar wrote: > > Currently str(slice(10)) returns "slice(None, 10, None)" > > > > If the start and step are None, consider not emitting them. Similarly > > slice(None) is rendered slice(None, None, None). > > > > When you're printing a lot of slices, it's a lot of extra noise. > > I have an alternative suggestion. Wouldn't it be nice if slice objects > looked something like the usual slice syntax? > > If you think the answer is No, then you'll hate my suggestion :-) > > Let's keep the current repr() of slice objects as they are, using the > full function-call syntax complete with all three arguments show > explicitly: > > repr(slice(None, None, None)) => "slice(None, None, None)" > > But let's make str() of a slice more suggestive of actual slicing, and > as a bonus, make slices easier to create too. > > str(slice(None, None, None)) => "slice[:]" > > Let the slice type itself be sliceable, as an alternate constuctor: > > slice[:] => returns slice(None) > slice[start:] => returns slice(start, None) > slice[:end] => returns slice(None, end) > slice[start::step] => returns slice(start, None, step) > > and so forth. (This probably would require changing the type of slice to > a new metaclass.) > > And then have str() return the compact slice syntax. > > At worst, the compact slice syntax is one character longer than the > optimal function syntax: > > # proposed slice str() > slice[:7] # 9 characters > > # proposed compact str() > slice(7) # 8 characters > > # current str() > slice(None, 7, None) # 20 characters > > > but it will be more compact more often: > > slice[1:] # 9 characters > > versus: > > slice(1, None) # 14 characters > slice(None, 1, None) # 20 characters > > > > > -- > 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/ > -- Keeping medicines from the bloodstreams of the sick; food from the bellies of the hungry; books from the hands of the uneducated; technology from the underdeveloped; and putting advocates of freedom in prisons. Intellectual property is to the 21st century what the slave trade was to the 16th.
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