This function must have the following header: def conv$\_$num$($num$\_$str$).$ This function takes in a string and converts it into a base $10$ number, and returns it$.$ It has the following specifications:

Must be able to handle strings that represent integers

Must be able to handle strings that represent floating$-$point numbers

Must be able to handle hexadecimal numbers with the prefix $0$x

Must be case insensitive $($both the prefix and what follows$)$

Negative numbers are indicated with a $-$ like $-0$xFF

Only integers are valid inputs for hexadecimal numbers $($i$.$e$.,$ no $0$xFF$\mathrm{.}02)$

The type returned must match the type sent. For example, if a string of an integer is passed in$,$ conv$\_$num must return an int.

Invalid formats should return None $($n$.$b$.$ this is not a string, but the actual None value$),$ including, but not limited to:

strings with multiple decimal points

strings with alpha that aren't part of a hexadecimal number

strings with a hexadecimal number without the proceeding $0$x

values for num$\_$str that are not strings or are empty strings

Some examples:

conv$\_$num$(\text{'}12345\text{'})$ returns $12345$

conv$\_$num$(\text{'}-123\mathrm{.}45\text{'})$ returns $-123\mathrm{.}45$

conv$\_$num$(\text{'}\mathrm{.}45\text{'})$ returns $0\mathrm{.}45$

conv$\_$num$(\text{'}123.\text{'})$ returns $123\mathrm{.}0$

conv$\_$num$(\text{'}0$xAD$4\text{'})$ returns $2772$

conv$\_$num$(\text{'}0$Xad$4\text{'})$ returns $2772$

conv$\_$num$(\text{'}0$xAZ$4\text{'})$ returns None

conv$\_$num$(\text{'}12345$A$\text{'})$ returns None

conv$\_$num$(\text{'}12\mathrm{.}3\mathrm{.}45\text{'})$ returns None

You are not permitted to use any of the following:

int$()$

float$()$

hex$()$

eval$()$

literal$\_$eval$()$