Sauli Olavi Arvila, 59, got in an argument with his "life partner" when she asked him to get her her methadone.

He put a teddy bear on her face, sat on her, and began punching her in the head.

The woman was in advanced stages of terminal lung cancer, and would die three weeks later due to the illness.

Chief Magistrate Lorraine Walker told Arvila that, as is typical in domestic violence offences, he, as a man, was already in a position of power and strength.

"That was made even more so because she was frail, tiny, and unwell," Ms Walker said.

The injuries would not have been serious on a healthy person, the court heard, but were exacerbated because of the illness.

The court heard the relationship was tense and emotional due to the woman's terminal illness, and Arvila submitted it was a one-off, with no evidence of past violence.

But prosecutor Anthony Williamson pointed to the woman's interview with police, in which she spoke of being beaten every time her partner took methamphetamine.

Mr Williamson said any right-minded member of the community would be quite distressed by the offence, and would find it "quite abhorrent".

He submitted imprisonment was the only sentence appropriate to reflect the seriousness of the crime.

Ms Walker agreed, and sentenced Arvila to eight months imprisonment.

Arvila will serve three months before the sentence is suspended, on condition he enter a good behaviour order for 12 months.

"I'm of the view that a sentence of imprisonment is the only one that reflects the seriousness of this offending," Ms Walker said.

Arvila's lawyer submitted the man had no criminal history of violence, and had significant health and mobility problems.

He argued those circumstances should warrant a full suspension of the jail sentence, something rejected by the court.

Arvila also claimed to be off drugs, and was living in settled accommodation.

"This was a one-off and it was a one-off in circumstances that hitherto had not existed in the past," his lawyer said.

"His life now is very different to what it was at the time of this assault."