Not being able to detect '-' character in regular expression [duplicate]

Question

I am trying to test whether a character is a special character or not.

It fails for '-' character when I write the following code:

import re

s = '-'
regex = re.compile('[!@#$%^&*()-+]')

if regex.search(s) == None:
    print("Not found")
else:
    print("Found")

Output>>Not found

However, if I change the position of the '-' character in the pattern as follows (line 3 of code), it works correctly

import re 

s = '-'
regex = re.compile('[!@#$%^&*()+-]')

if regex.search(s) == None:
    print("Not found")
else:
    print("Found")

Output>>Found

What is causing this difference and how can I make sure that the characters will be detected?

Answer 1

- is treated as a special character if it is not the last or the first character in a range and not escaped. So:

• [-19] or [19-] or [1\-9] is -, 1 or 9, but
• [1-9] is anything between 1 and 9, inclusive, but not - itself.