Is there any way to clear a surface from anything that has been blitted to it?
If what you want is to make a pygame Surface object "clean", that is erase all images blited to it, to blit new images to it every game loop and keep the peer pixel alpha without creating a new surface, you can fill it, but instead of a solid color, use a transparent color
from pygame import Color, Surface
empty = Color(0,0,0,0) #The last 0 indicates 0 alpha, a transparent color
field = Surface((width, height), flags=SRCALPHA)
#Inside the game loop
field.fill(empty)
*Sorry is my english is bad, still learning