Python 3.9.x | Cannot 'return' variable with user entry validation - function

Question

I'm having problems getting my code to 'return' one of the option strings correctly.
If the user inputs one of the string options correctly the first time through, then the 'return' value comes back perfectly fine when going through the 'while' to 'if/elif' statements. No problem.
However, if the user DOES NOT input the data correctly the first time through, I'm trying to catch that with my final 'else' statement and then begin the function again. However, the second/third/ect time through, even if the user inputs a valid selection, the 'return' type is None and the value returned is None.
So, my user validation is missing something. Any thoughts?
#Global variable initialization
mainSelection = str(None)
#Santa's Christmas Card List Main Menu function
def XmasMainMenu(mainSelection):
print('')
print('How may the elves be of service today?')
print('')
print('\"PRINT\" - Print out the Christmas card list from the database.')
print('\"ADD\" - Add nice recipients information to the Christmas card list.')
print('\"SEARCH\" - Search the database for information.')
print('\"DELETE\" - Remove naughty recipients from the Christmas card list. ')
print('\"EXIT\" - Exit the program without any printing or changes to the database.')
print('')
mainSelection = input('Please enter your selection: ')
mainSelection = mainSelection.lower()
print(type(mainSelection), mainSelection)
#Selection return value
while mainSelection != None:
if mainSelection == 'print':
print('|| Will print out the Xmas Card List ||')
return mainSelection
elif mainSelection == 'add':
print('|| Will prompt user to add information to the DB ||')
return mainSelection
elif mainSelection == 'search':
print('|| Will prompt user to search the information in the DB ||')
return mainSelection
elif mainSelection == 'delete':
print('|| Will prompt the user to delete recipients from the DB ||')
return mainSelection
elif mainSelection == 'exit':
print('|| Will exit the user from the program with no changes')
return mainSelection
elif mainSelection == 'drop table':
print('|| Will call the XmasTableDrop function ||')
return mainSelection
else:
print('')
print('Input Error: Please enter a valid selection above!')
print('Try again...')
print('')
print(type(mainSelection), mainSelection)
break
XmasMainMenu(mainSelection)
Program Launch
User input correct, 'return' value is correct
1st user input invalid. Error message is received, the function starts over again. 2nd user input valid --> however, the 'return' type is None and the value is None (this is what I need to fix, but cannot figure out).

Answer 1

This is a typical "new programmer" mistake. Do not call a function within the function itself unless you know what recursion is and how it works. When a called function returns it returns to the function that called it. What happens is:
XmasMainMenu is called from the top-level script.
...user enters an incorrect value...
XmasMainMenu calls XmasMainMenu again.
...user enters a correct value....
XmasMainMenu (2nd call) returns to XmasMainMenu (1st call)
The return value is not assigned to anything, so is lost.
Now at the end of the function with no return, so returns default None.
top-level script receives None.
Instead, wrap your code in a while True: and break when you get a correct value, then return that (pseudo-code):
def XmasMainMenu():
while True:
print menu # this could be outside while if you don't want to re-print menu.
selection = input()
if selection valid:
break # exit while loop
else:
prompt user to enter valid input.
return selection