input: Write a function to calculate the Euclidean distance between two points on a two-dimensional plane. The function should take four parameters, x1, y1 for the first point and x2, y2 for the second point, and return the calculated distance as a float.
  assert distance(3, 4, -9, -2)==13.0
  assert distance(0, 0, 3, 4)==5.0
  assert distance(-2, -3, -4, -5)==2.8284271247461903
  assert distance(1, 1, 1, 1)==0.0
  assert distance(5, -7, -3, 2)==12.041594578792296
output: def distance(x1, y1, x2, y2):
      return ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** 0.5