input: Write a function to compute the area of a circle with the given radius. If the radius is not a positive number, return None. Use the math.pi constant for π.
  assert area_circle(5) == 78.54
  assert area_circle(0) == None
  assert area_circle(-3) == None
  assert area_circle(10) == 314.16
  assert area_circle(1) == 3.14
  
  import math
  
  def area_circle(radius):
   if radius > 0:
   return math.pi * (radius ** 2)
   else:
   return None
output: import math
  
  def area_circle(radius):
      if radius > 0:
          return math.pi * (radius ** 2)
      else:
          return None