Jorge, next time you have questions about how to use a module (and struct is fairly advanced), please ask on an appropriate forum, such as python-list.  Then Steven's nice answer could be read by 100s of people instead of likely less than 10.

I looked as the struct doc to see if I thought it needs anything and decided I agree with Stephen that not.  Struct can pack and unpack various IEEE binary floating point formats.  Anyone doing serious work with such knows that they include infinities and nans.