There are over 3000 species of snakes worldwide of which about 600 are venomous. Of these 600 many are either too small or have too weak a venom to be lethal to humans. When it comes to determining the most deadly snakes in the world it is very difficult because there is a difference between the most venomous, and most dangerous. Being the most dangerous considers behaviour, distribution, proximity to human settlements and toxicity. While the tests that determine the toxicity (LD50 test) of a snakes venom is done using the reaction and the time taken to kill mice as a result of subcutaneous injection. Drop for drop the venom of the western or inland taipan is regarded by far as the most toxic of all snakes (land or sea) yet it is not regarded as being a very dangerous snake due its remote distribution and non-confrontational nature. There have been no recorded human fatalities from the western taipan envenomation.
One thing is for sure Australia has several snakes that are very capable of inflicting lethal bites if left untreated. In the above test the top six most toxic land snakes in the world are all Australian. The western taipan, the eastern brown snake, coastal taipan, the black tiger snake, mainland tiger snake and the Western Australian tiger snake.
Danger wise is a different story as the method of determining the most dangerous is slightly less scientific and relies upon opinion to some degree, therefore it is unlikely that you will ever find two publications listing the same 10 most deadly snakes in the same order. However you will see that there are several Australian snakes that make the list repeatedly and they are; the eastern brown snake, the taipan, western taipan, death adder, tiger snakes and less often, the red-bellied black snake.
Pythons are regarded as non-venomous snakes that kill prey by constriction rather than envenomation. In Australia there are many pythons the largest being the amethystine or scrub python which is ranked as the sixth largest snake in the world with an official record dimension of 90kgs and 7.2 metres. Unofficial measurements put this snake in the 8 metre range but it generally only grows to about 5 metres. Another large Australian python is the olive python and in particular the subspecies from the Pilbara region of Western Australia.