Implements function that returns the sum of a number's digits

[sheareralexj]

This ticket adds a function to return, given a number and base, the sum of digits of that number in that base. For example, this enables:

sage: digit_sum(4412, b=10)
11

sage: digit_sum(4412, b=6)
12

Component: number theory

Author: Alex Shearer

Branch/Commit: u/gh-sheareralexj/implements_function_that_returns_the_sum_of_a_number_s_digits @ a8e7f14

Issue created by migration from https://trac.sagemath.org/ticket/28100

[sheareralexj]

Branch: u/gh-sheareralexj/implements_function_that_returns_the_sum_of_a_number_s_digits

[sheareralexj]

New commits:

a8e7f14

28100: Implements function that returns sum of digits of `n`

[sheareralexj]

Author: Alex Shearer

[sheareralexj]

Commit: a8e7f14

[videlec]

comment:3

What is the advantage of this function compared to

sage: sum(n.digits(b))

?

[sheareralexj]

comment:4

Replying to @videlec:

What is the advantage of this function compared to

sage: sum(n.digits(b))

?

There is no real advantage, although we thought it makes sense to have a dedicated sum of digits function implemented.

[kedlaya]

comment:5

While we are at it, since digits is a method of Sage integers rather than a top-level function, maybe this should be also?

As an aside, it would have been more Pythonic if once upon a time, digits had been written to return an iterator rather than a list. But that would be a painful change to make now.

[jhpalmieri]

comment:6

Replying to @videlec:

What is the advantage of this function compared to

sage: sum(n.digits(b))

?

A related question: what are the disadvantages to the proposed function digit_sum? I don't know if this function is of enough general interest to warrant being defined at the top level, rather than being a method for integers and/or a function which has to be imported if you want to use it. There have been some efforts to remove underused items from the top-level name space (#25383), and I think there should be a good reason for adding a new one.

tl;dr: why not instead implement 4412.digit_sum(b=10)?

[embray]

comment:7

Ticket retargeted after milestone closed

[jplab]

comment:8

Replying to @jhpalmieri:

Replying to @videlec:

What is the advantage of this function compared to

sage: sum(n.digits(b))

?

A related question: what are the disadvantages to the proposed function digit_sum? I don't know if this function is of enough general interest to warrant being defined at the top level, rather than being a method for integers and/or a function which has to be imported if you want to use it. There have been some efforts to remove underused items from the top-level name space (#25383), and I think there should be a good reason for adding a new one.

tl;dr: why not instead implement 4412.digit_sum(b=10)?

+1

[videlec]

comment:9

Unless the digit_sum provides a much faster way to perform the computation than sum(n.digits(b=10)), I don't see why we should add such method to integers. I don't think a method is more convenient. sum and prod are very much standard. If some people think they are not, then one can add an extra example to the documentation of Integer.digits.

Users would better learn a bit of Python rather being lost in an endless Sage namespace (that applies to the main namespace but also to objects).

[kedlaya]

comment:10

As I commented earlier, if n.digits had been written in the first place to return an iterable rather than a list, then there would be no speed differential.

But maybe a better solution would to be modify n.digits to give it an optional argument to return that iterable. Then sum(n.digits(b=10,iterable=True)) would be as fast as anything else.

And honestly, I think the use case for which this makes a difference is quite narrow.

[mkoeppe]

comment:11

Batch modifying tickets that will likely not be ready for 9.1, based on a review of the ticket title, branch/review status, and last modification date.

[mkoeppe]

comment:13

Setting new milestone based on a cursory review of ticket status, priority, and last modification date.

[mkoeppe]

comment:14

Setting a new milestone for this ticket based on a cursory review.

[mkoeppe]

comment:15

Stalled in needs_review or needs_info; likely won't make it into Sage 9.5.