You can simply put sprite_sheet.get_image into the loop:

self.walk_right = []

for num in range (1,10):
    walk_right_temp = sprite_sheet.get_image(num,11,sprite_width,sprite_height,1.25,0)
    self.walk_right.append(walk_right_temp)

Or use python's list comprehension:

self.walk_right = [sprite_sheet.get_image(num,11,sprite_width,sprite_height,1.25,0) for num in range (1,10)]

You can simply put sprite_sheet.get_image into the loop:

self.walk_right = []

for num in range (1,10):
    walk_right_temp = sprite_sheet.get_image(num,11,sprite_width,sprite_height,1.25,0)
    self.walk_right.append(walk_right_temp)

Or use python's list comprehension:

self.walk_right = [sprite_sheet.get_image(num,11,sprite_width,sprite_height,1.25,0) for num in range (1,10)]

Or, It is indeed possible to find local/global/member variables by string if really necessary(Most of the time you don't need to do this):

self.__dict__["walk_right"]= []
for num in range (1,10):
    self.__dict__["walk_right"].append(locals()[f'walk_right_{num}'])