finding angle between three points on a 2d graph

[Gribouillis]

It is almost correct. The order of the points matters

import math

def angle3pt(a, b, c):
    """Counterclockwise angle in degrees by turning from a to c around b
        Returns a float between 0.0 and 360.0"""
    ang = math.degrees(
        math.atan2(c[1]-b[1], c[0]-b[0]) - math.atan2(a[1]-b[1], a[0]-b[0]))
    return ang + 360 if ang < 0 else ang

print(angle3pt((5, 0), (0, 0), (0, 5)))

Output:
90.0

This function will not throw an error if a==b or c==b because math.atan2(0,0) returns 0.0. It would probably be a good idea to add this in the function, something like

    if b in (a, c):
        raise ValueError("Undefined angle, two identical points", (a, b, c))