Does a penalty assessment have an obligation to be imposed on an inmate who has pleaded guilty to a charge of assault?

Furthermore, the imposition of a penalty assessment pursuant to Penal Code section 1464, subdivision (a) is mandatory. Trial courts are given discretion under subdivision (d) of section 1464 not to impose the penalty assessment where an inmate remains in prison and the payment of the assessment "would work a hardship on the person convicted or his or her immediate family." Otherwise, the trial court has an obligation to impose a penalty assessment. (People v. Heisler (1987) 192 Cal.App.3d 504, 506-507, 237 Cal.Rptr. 452.)