A Tasmanian woman has admitted to stealing more than 50 blocks of chocolate and pulling a knife on a shop assistant who tried to stop her.

Carol Anne Devine, 43, of Derwent Park has pleaded guilty in the Supreme Court in Hobart to one count of stealing and one count of assault.

She tried to leave an Eastlands supermarket in March without paying for more than 50 200-gram blocks of chocolate and several hair care products.

When a shop assistant asked to search Devine's bag, she pulled a folding knife out of her bra and said "leave us alone or I'll knife you".

Crown Prosecutor Allison Shand said Devine has 39 prior convictions for stealing and has been sent to jail a number of times.

Devine's lawyer said her client only intended the knife as a threat and admits the crime was stupid.

She said Devine has a gambling addiction and regards jail as a refuge from her violent son.

She will be sentenced next week.