Code to ask for user string, then display the output
More elegant way to check if a string is empty
Read here

if not s_string:
    sys.exit()


You don't need a sys.exit(), just let the program exit on its own.

if s_string:
    print(s_string)

# the program will exit here anyway.  


sys.exit() has some side-effects like killing the python interpreter, which might have some undesirable effects. Read here

You don't even need to check if the string is empty

print(s_string) # If string is empty, will print nothing except for a newline.


Name s_string just s or string. 

It doesn't detract from the readability of the code, and makes it more pretty and easier to type(and read)

Most people tend to prefer double quotes " for string literals Read Here