When searching for code to calculate the circle out of 3 points it leads me to this code:

def circleRadius(b, c, d):
temp = c[0]**2 + c[1]**2
bc = (b[0]**2 + b[1]**2 - temp) / 2
cd = (temp - d[0]**2 - d[1]**2) / 2
det = (b[0] - c[0]) * (c[1] - d[1]) - (c[0] - d[0]) * (b[1] - c[1])

if abs(det) < 1.0e-10:
return None

# Center of circle
cx = (bc*(c[1] - d[1]) - cd*(b[1] - c[1])) / det
cy = ((b[0] - c[0]) * cd - (c[0] - d[0]) * bc) / det

radius = ((cx - b[0])**2 + (cy - b[1])**2)**.5