[Numpy-discussion] [help needed] associativity and precedence of '@'
Nathaniel Smith
njs@pobox....
Thu Mar 20 12:25:06 CDT 2014
On Wed, Mar 19, 2014 at 7:45 PM, Nathaniel Smith <njs@pobox.com> wrote:
> Okay, I wrote a little script [1] to scan Python source files look for
> things like 'dot(a, dot(b, c))' or 'dot(dot(a, b), c)', or the ndarray.dot
> method equivalents. So what we get out is:
> - a count of how many 'dot' calls there are
> - a count of how often we see left-associative nestings: dot(dot(a, b), c)
> - a count of how often we see right-associative nestings: dot(a, dot(b, c))
>
> Running it on a bunch of projects, I get:
>
> | project | dots | left | right | right/left |
> |--------------+------+------+-------+------------|
> | scipy | 796 | 53 | 27 | 0.51 |
> | nipy | 275 | 3 | 19 | 6.33 |
> | scikit-learn | 472 | 11 | 10 | 0.91 |
> | statsmodels | 803 | 46 | 38 | 0.83 |
> | astropy | 17 | 0 | 0 | nan |
> | scikit-image | 15 | 1 | 0 | 0.00 |
> |--------------+------+------+-------+------------|
> | total | 2378 | 114 | 94 | 0.82 |
>
Another way to visualize this, converting each contiguous "chain" of calls
to np.dot into a parenthesized expression, and then counting how often we
see each pattern.
1943 (_ @ _)
100 ((_ @ _) @ _) # left
86 (_ @ (_ @ _)) # right
2 (_ @ ((_ @ _) @ _))
2 (((_ @ _) @ _) @ _) # left
1 ((_ @ (_ @ _)) @ _)
1 ((_ @ _) @ (_ @ _))
1 (((_ @ _) @ _) @ (_ @ _))
1 ((_ @ ((_ @ _) @ _)) @ _)
1 ((_ @ _) @ (_ @ (_ @ _)))
(This is pooling scipy/nipy/scikit-learn/statsmodels.) I've noted the 3
different patterns that have a consistent associativity.
>From this I'm leaning towards the conclusions that:
- Expressions with complex parenthesization do happen, but probably not
often enough to justify elaborate stuff like my 'chaining' proposal -- only
8.7% of these cases involve more than one @.
- There's very little support here for the intuition that
right-associativity is more useful than left-associativity on a day-to-day
basis.
--
Nathaniel J. Smith
Postdoctoral researcher - Informatics - University of Edinburgh
http://vorpus.org
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