input: Write a function to calculate the distance between two points on a two-dimensional plane given their x and y coordinates. The function should take four arguments: x1, y1, x2, and y2, and return the calculated distance as a float.
  assert distance(3, 4, -9, -2) == 13.416407864998739
  assert distance(0, 0, 0, 0) == 0.0
  assert distance(1, 1, 4, 5) == 5.0
  assert distance(-3, -4, -7, -10) == 7.211102550927978
output: def distance(x1, y1, x2, y2):
      return ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** 0.5