Are a pythons poisonous

It depends upon the species. Most python species are smallish, and are not dangerous. Large species such as the Australian scrub python, olive python, Burmese python and reticulated python are all known to have attacked people and are known to inflict horrible injuries and even death!
It depends what specie of Python you're talking about. The smaller Pythons - such as the Royal python (Python regius) can give a nasty bite - but are not capable of harming people(due to their size). However - larger species - such as the African Rock Python (Python sebae sebae) are certainly large enough to swallow a small child.