NameError Traceback $($most recent call last$)$

Cell In$[2],$ line $26$

$23$ model.add$($layers$.$Flatten$($input$\_$shape$=(28,28)))$

$25$ # Tune the number of hidden layers

$--->26$ for i in range$($hp$.$Int$(\text{'}$num$\_$layers', $1,4))$:

$27$ # Tune the size of the hidden layers

$28$ model.add$($layers$.$Dense$($units$=$hp$.$Int$(\text{'}$units$\_\text{'}+$ str$($i$),32,256,32),$

$29$ activation$=$'relu'$))$

$31$ # Set dropout for all hidden layers except the last one

NameError: name $\text{'}$hp$\text{'}$ is not defined

how to remove this error?