input: Write a function to calculate the distance between two points with coordinates (x1, y1) and (x2, y2). Return the distance as a float value.
  assert distance_between_points(2, 7, 4, 9)==math.sqrt(8)
  assert distance_between_points(0, 0, 3, 4)==5.0
  assert distance_between_points(-1, -1, 1, 1)==2*math.sqrt(2)
  assert distance_between_points(0, 0, 0, 0)==0.0
  assert distance_between_points(-5, -10, 5, 10)==10*math.sqrt(5)
output: import math
  
  def distance_between_points(x1, y1, x2, y2):
      return math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)