我正在尝试制作一个程序，但我不知道我做错了什么

Question

I am trying to make a program that asks the user a file input with the prompt "New file name" and the program should work like this and if the name has any form and/or combinations of "importantdocument.text" and i try the new forms and how can i make the code work easier than keep putting {variable} != {form of importantdocumant.txt} can anyone help to see what i'm doing wrong or write a code that does what the program is supposed to do? thanks ahead of time.

my program

a = input('New file name: ')
if a != 'ImportantDocument.txt' and a != 'importantDOCUMENT.txt' and a != 'IMPORTANTDOCUMENT.TXT' and a != 'importantdocument.txt' and a != '':
    print('That name is allowed.')
elif a == 'ImportantDocument.txt' or a == 'importantDOCUMENT.txt' or a == 'IMPORTANTDOCUMENT.TXT' or a == 'importantdocument.txt':
    print('That file already exists.')

what the programs supposed to output

New file name: lessimportantdocument.txt
This name is allowed.

or

New file name: ImPorTaNtdoCumenT.tXt
That file already exists.

Answer 1

    a = input('New file name: ')
    k = a.upper()
    if k != 'IMPORTANTDOCUMENT.TXT':
           print("That name is allowed")
    if k == 'IMPORTANTDOCUMENT.TXT':
           print("That file already exists")

Answer 2

If you are wanting to check if the file exists, you could try read it. I've not tested this but it should work.

file_location = 'C:/Folder/' + a

try:
    with open(file_location , "r") as f:
        f.read()
except IOError:
    print("That file already exists")
else:
    print("That name is allowed")

If you literally just wanting to neaten up the code you have currently, then Mohd's answer is good.