Want to know how to have game1.py, run game1a.py once level is completed (code attached)

Question

When completing a stage in game1, I want the code to now progress and open game1a.py and continue playing till completed, then move onto game1b.py

I also want in game1a.py or game1b.py that if I loose it take me back a game level e.g game1a.py back to game1.py, game1b.py to game1.py and run the game without having to run the command 'python3 game1.py' again, unless the user chooses to exit.

I am a beginner and have watch a number video's and reviewed comments, but still having trouble understanding the code requirements.

#My code message_display, which then should open and run game1a.py#

import file ('game1a.py')

def message_display_wh(text): largeText = pygame.font.Font('freesansbold.ttf', 40)
TextSurf, TextRect = text_objects(text, largeText)
TextRect.center = ((display_width/2),(display_height/2))
gameDisplay.blit(TextSurf, TextRect)

pygame.display.update()   

time.sleep(1)

#require code here to enter game1a.py now that the user has completed the level.

any help would be greatly appreciated.