[Python] Why is the function being called twice?

Here's the code:

truthful:

cart = {}
subMenuItems = {}
import menu_2
menu_2.mainmenu()


Main:

def mainmenu():
ID = ("FB10", "FS20", "FD30", "FD40", "FC50")
print(ID)
choice = input("> ").upper().strip()
while True: #vailidates input
if choice not in ID:
print("Please choose a valid selection")
choice = input("> ").upper().strip()
elif choice in ID:
# print(f"You've selected {choice}")
import sub_menu_5
sub_menu_5.assign_sub_menu_items(choice)
sub_menu_5.sub_menu()
break


Sub:


def input_stuff():
import truthful
while True:
userInput = input('> ').strip().upper()

if userInput in truthful.subMenuItems:
return userInput

elif userInput == '1' or userInput == 'MAIN MENU':
return userInput

elif userInput == '2' or userInput == 'CART':
return userInput

else:
print('Invalid input. PLease try again')

def sub_menu():
display_menu() #imports subMenuItems from truthful
stuff = input_stuff()
print(stuff)

import cart_3,menu_2
if stuff == '1' or stuff == 'MAIN MENU':
print('Entering Main Menu')
menu_2.mainmenu()
elif stuff == '2' or stuff == 'CART':
print('Entering Cart')
cart_3.cart_display()
valid = True
while valid:
try:
cart_3.cart_input()
valid = False
except ValueError:
print('Invalid input, try again.')
else: ...






def cart_input(): #does all the input stuff within the cart
import truthful
if truthful.cart != {}: #if cart not M.T.
userInput = float(input('> ')) #we're not cheesing ValueError disappointed
if userInput == 1:
...
if userInput == 2:
...
elif userInput == 3: #prints main menu. pls add menu function.
import menu_2
print('Entering Main Menu: ')
menu_2.mainmenu()
elif userInput == 4: #prints checkout. a
checkout()
else:
print('Invalid input.')
cart_input()
else: #when cart from truthful is empty
print('Enter anything to return to the Main Menu.')
input('> ')
import menu_2
menu_2.mainmenu()

def checkout():
import truthful
import menu_2
import Discount
...
while True:
checkoutInput = input('> ').lower().strip()
if checkoutInput == '1' or checkoutInput == 'checkout':
print('Checkout complete!')
print('Would you like to order again?')
#if yes then k-
return
elif checkoutInput == '2' or checkoutInput == 'main menu':
print('Entering Main Menu')
menu_2.mainmenu()
elif checkoutInput == '3' or checkoutInput == 'cart':
print('Entering Cart')
cart_display()
finalValid = False
while finalValid == False:
try:
cart_input()
finalValid = True
except ValueError:
print('Invalid input, try again')
else:
print('Please enter a valid input.')


When I input an ID for 'choice = input("> ")' for the first time, mainmenu() runs again.

When I input 1 for checkoutInput, it runs the print statements within the if, and then runs subMenu().

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