I have a regular expression that matches alphabets, numbers, _ and - (with a minimum and maximum length).

^[a-zA-Z0-9_-]{3,100}$

I want to include whitespace in that set of characters.

According to the Python documentation:

Character classes such as \w or \S are also accepted inside a set.

So I tried:

^[a-zA-Z0-9_-\s]{3,100}$

But it gives bad character range error. How can I include whitespace in the above set?

The problem is not the \s but the - which indicates a character range, unless it is at the end or start of the class. Use this:

^[a-zA-Z0-9_\s-]{3,100}$