input: Write a python function to calculate the distance between two points.
  assert distance_between_points(2, 7, 4, 9) == 2.8284271247461903
  assert distance_between_points(0, 0, 3, 4) == 5.0
  assert distance_between_points(1, 1, 4, 5) == 5.0
output: def distance_between_points(x1, y1, x2, y2):
      import math
      return math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)