Method to create `Vec2d` from magnitude and angle

[aatle]

Often, I am given a magnitude and an angle in radians, and I need to create a vector from this.
The current ways to do it:

Vec2d(magnitude, 0.0).rotated(angle)
Vec2d(cos(angle), sin(angle)) * magnitude

It would be nice to have a classmethod that can do this more cleanly:

@classmethod
def from_polar(cls, r, theta):
    return cls(cos(theta) * r, sin(theta) * r)

Vec2d.from_polar(magnitude, angle)

I count 6 possible places I could use this in my codebase.
Example:
Apply an impulse of x magnitude, at an angle pointing towards the mouse cursor.

[viblo]

Sounds reasonable. I did a quick check and both pygame and pyglet has such a method on their vector classes.
Something like this

@staticmethod
def from_polar(length, angle) -> "Vec2d":
    """Create a new Vec2d from a length and an angle (in radians)

    >>> Vec2d.from_polar(2, 0)
    Vec2d(2, 0)
    >>> pymunk.Vec2d(2, 0).rotated(0.5) == Vec2d.from_polar(2, 0.5)
    True 
    """
    return Vec2d(cos(angle) * length, sin(angle) * length)

(staticmethod since the other ones are also static, and length/angle as names since that is the names already used in other vec2d methods)

[viblo]

Thanks for this, next release of pymunk will contain a from_polars method :)