variable from batch file to python [duplicate]

**Updated because of comments

I am trying to pass a variable from a batch file to my python files. I am getting a n unexpected result; my code:

In my batch file:

SET variablename = 'name'
python 01_preparing.py %variablename%

In my python file

import sys

print('Argument:', sys.argv[1])

Result is

Traceback (most recent call last):
File "01_preparing.py", line 5, in <module>
print('Argument:', sys.argv[1])
IndexError: list index out of range

Started out with this example: Sending arguments from Batch file to Python script