cmath.rect accepts a negative modulus

[JMB]

The function cmath.rect(r, phi) accepts negative values for r. For example: cmath.rect(-1, 0) returns (-1-0j).

The returned value is according to what is explained in the function documentation: r*(math.cos(phi) + math.sin(phi)*1j), but given that a negative modulus makes no sense, shouldn't the function return an Exception?

[Gribouillis]

given that a negative modulus makes no sense, shouldn't the function return an Exception?

The documentation does not speak about modulus. It speaks about polar coordinates. For example the doctstring

Output:
Help on built-in function rect in module cmath:

rect(r, phi, /)
    Convert from polar coordinates to rectangular coordinates.

It is often accepted in mathematics that polar coordinates allow a negative radius. This is the case when studying plane curves in polar coordinates for example. Interestingly, a way to find the correct modulus and arguments is to compose with cmath.polar()

>>> import cmath
>>> cmath.polar(cmath.rect(-1, 0))
(1.0, -3.141592653589793)  # modulus 1, angle -pi

Should it raise an exception? Well let's say it is a design choice. You can write your own wrapper to raise an exception if the radius is negative!

[JMB]

Thanks for your prompt answer! I think I'll opt for the wrapper, given that I use complex numbers in electrical engineering, to represent A.C. voltages and currents.