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