$3.$ You're going to write an interactive calculator! User input is assumed to be a formula that consist of a number, an operator $($at least $+$ and $-),$ and another number, separated by white space $($e$.$g$.1+1).$ Split user input using str$.$split, and check whether the resulting list is valid:

If the input does not consist of $3$ elements, raise a FormulaError, which is a custom Exception. Try to convert the first and third input to a float $($like so:

float$\_$value $=$ float$($str$\_$value$)).$ Catch any ValueError that

occurs, and instead raise a FormulaError. If the second input is not $\text{'}+\text{'}$ or$\text{'}-\text{'},$ again raise a FormulaError. If the input is valid, perform the calculation and print out the result. The user is then prompted to provide new input, and so on$,$ until the user enters quit. $($Python Program$)$