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 (_ @ _)

1943 (_ @ _)

100 ((_ @ _) @ _) # left

86 (_ @ (_ @ _)) # right

2 (_ @ ((_ @ _) @ _))

2 (((_ @ _) @ _) @ _) # left

1 ((_ @ (_ @ _)) @ _)

1 ((_ @ _) @ (_ @ _))

1 (((_ @ _) @ _) @ (_ @ _))

1 ((_ @ ((_ @ _) @ _)) @ _)

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 @.

- 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