When Soper told him to leave, Edwards lunged at him with a 30cm serrated hunting knife which had been hidden in his jacket.
It went through Soper's forearm to such a depth that it came out the other side.
Soper's father, Newstalk ZB political editor Barry Soper, was present for the sentencing at Wellington District Court today.
During sentencing, Judge Peter Hobbs repeatedly stressed that he was legally bound to take into account the eight months served in jail on remand, and four months on electronically monitored bail, while Edwards was waiting to be sentenced.
"I have read the victim impact statement, and it is clear the victim continues to suffer physically from your actions.
"It is not yet certain whether he will fully recover. It is possible he will continue to suffer some disability from your actions."
Judge Hobbs noted Soper had also suffered financial and emotional impacts, which he said was not surprising.
"There was an element of premeditation on your behalf.
"You took with you into a city precinct a 30cm hunting knife. You waited for the victim outside.
"The use of a hunting knife is serious, it is potentially a lethal weapon. It is also worth noting that at the time you were on a community work sentence."
Judge Hobbs admitted the sentence for four months' home detention would not appear to be enough, if looked at in isolation.
"A deterrent sentence is required, people cannot carry knives in public and use them to inflict injuries such as this.
"However, you have already effectively served a 16-month sentence of imprisonment, on remand, following your arrest.
"Had you not already spent 16 months effectively in prison, plus four months home detention, I would be sentencing you to prison. But because you have successfully completed that I will sentence you to four months home detention."
After the sentencing, Barry Soper said the family was relieved the outcome hadn't been more serious for his son Henry.
"Even though his injury was serious enough, but he is fortunately on the mend.
"I have never felt a custodial sentence should be automatically imposed, and although a random assault with such a vicious weapon would generally result in incarceration, the outcome here was in my view a fair one.
"Henry has received an apology letter from Edwards, who we are told has turned his life around.
"If that is truly the case, then justice has been well served.
"I would like to thank the police for the way they have handled this matter and the sensitivity they have shown to my family."
Edwards' home detention requires 24-hour curfew.
He will also pay reparations of $3000, and serve 200 hours of community work.
