'''
Assembles the name of a file called "x.txt"
The literal string 'x' is used for this minimal example, but the issue
was originally encountered taking an arbitrary name from argv and seeing
if it needed an extension.
'''

import os

file_name = os.path.normcase('x') #"file_name = 'x'" fixes problem
if not os.path.isfile(file_name): #"if True:" fixes problem
    x = file_name + '.txt'
    file_name = file_name + '.txt'
#"file_name = file_name.encode('utf8').decode('utf8')" fixes problem
print('file_name exists: ' + str(os.path.isfile(file_name)))
print('x exists: ' + str(os.path.isfile(x)))
print('file_name == x: ' + str(file_name == x))