Snakes are definitely out and about in summer more than winter, though I have seen the odd straggler right up until January sometimes. In cold weather and generally during the cold months of winter they go to ground. We have sunny stone walls in the garden, they climb in each year between the stones when it starts getting cold to keep warmish.
I have though seen a bamboo snake in the middle of winter in the hedge, it was very lethargic as it hadn't got enough warmth from the weak sun to make it active, so was easy to pick up with a stick and place out of harms way. Not advisable unless you know snakes, two of my dogs have had very bad bites from these snakes. How dangerous a bite is, all depends on how my venom they pump into the bite. It can be very nasty with rapid swelling and tissue death leaving large wounds and or the dog can suffocate if bitten around the neck or head area as the head and throat will swell up twice the size, then on other occastions it might hardly pump anything in there and the dog or victim will feel nothing, though always treat it as dangerous.
This snake is also never in a hurry even when spotted and prefers to wait in ambush, so is quite a danger in thick areas of shrub and trees. Do not confuse it with other bright green harmless snakes, that most are, this one has a bright red tail tip, plump emerald green body and large for its size triangular head with a thin wiry neck, it is not the largest of snakes either.
Most other snakes are very skittish though and will "see" you a long time before you are lucky enough to see them, and move out of the way.
I have only ever seen a python once and it was completely black, quite rare, though I believe now that pythons in general might be quite common. I have seen most of the other species on numerous occasions right here in my garden. If you see any and can identify them make a report to the "Porcupine" site, as it is a very helpful tool in researching these vital animals.