feat(series): #1098 arithmetic addition

[cmp0xff]

This PR is motivated by #1273 (review).

Comprehensive plan (maybe in another PR)

Inspired by #1093, one can draft the following comprehensive plan for all possible combinations of the left arithmetic operand, the binary arithmetic operator and the right arithmetic operand.

Left operand

• Series[Any]
• Series[int]
• Series[float]
• Series[complex]

Binary arithmetic operators

Include their right-version and functional version. In add we give a full example. We follow the official documentation.

• __add__, __radd__, add, radd
• __truediv__
• __floordiv__
• __pow__
• __mod__
• __mul__
• __sub__

Right operand

• Scalar
• Sequence
• numpy arrays
• Series

Draft of a plan

• We can have 4 ~ 5 test scripts for each left operand
• In each test script, we can have 7 test functions for each binary arithmetic operator
• In each test function, we test on all right operands. Do not forget the possible four variations, see the example of add.

Checklist

• Closes Addition of a Series[int] with a complex returns Series[unknown] #1098, as stated in the title.
• Tests added: Please use assert_type() to assert the type of any return value

[loicdiridollou]

Looks like great progress here!

[cmp0xff]

Hi @twoertwein @loicdiridollou , I am making just minimal changes in __add__ now, and trying to understand the behaviour of self: typing.

May I ask why Series[Any] + int now gives Series[int]? From my point of view, what I added is that only Series[int] + int gives Series[int], and Series[Any] as the left operand is irrelevant. Thanks.

[twoertwein]

I think for Any/unknown, the overload order matters, the int overload is now the first one.

[twoertwein]

I believe I had a PR or issue where the overload order prevented me when I tried to remove TimestampSeries - unfortuntely, I can't find the PR/issue.

[cmp0xff]

Hi @twoertwein , thanks for the reply. I have specified self: Series[int], so that for Series[Any] the first overload should not be triggered.

[twoertwein]

type checkers match the first matching overload, I believe Any/unknown matches anything/the first overload

[twoertwein]

here is an example where we had issues in the past with the overload order with any/unknown: #571 (comment)

[cmp0xff]

I think now I understand it better. Is the current MR the direction to go? I just need to add combinations of overloads.