[pygame] how to copy a surface to an other surface with alpha value?

["flyaflya" <flyaflyaa@xxxxxxxxx>]

I want to join some surfaces to a new big surface with alpha cannel, I want the new surface has  same pixels(inclue r,g,b and alpha value) as the pixels on the source surfaces.

my code as follow:

 

surf = pygame.Surface((200,200))

surf.blit(surf1, (0,0))

surf.blit(surf2, (0,100))

.....

 

but these codes can't copy alpha value to the new surface.how can I deal with it?