I wanted to know that the connotation of this phrase:“be a glutton for sth” is positive or negative? Can I use it in statements, which are related to my interest,like:”I’m a glutton for painting.”
If you are a glutton, you eat to excess. It is strictly negative.
Figuratively, being a glutton means you consume something. You could, perhaps, say "I'm a glutton for art. I spend hours every day walking around art galleries". You are "consuming too much art". It would be odd to say "she is a glutton for painting", since this is productive, not consumptive.
There is an idiom: "a glutton for punishment". It means a person who is always eager to undertake hard or unpleasant tasks. It could be used in a rather ironic way about yourself.