All the above posts, very good advice for you, commander. I don't have a lot to add to it except maybe to give you some perspective changes.
Here goes:
First, Maximize your maximums, minimize your minimums, I always say.
Second, your expectations of the Python may have been too high. E.D. is a high-tech, rock-paper-scissors game. From what I've experienced, seen, and read, there is no one ship that is invulnerable. Each has strengths and weaknesses, and you must learn them. I first learned this when I watched a little kid's video titled, "Big Ships Are Easy", where he targeted an Anaconda's power supply, and very quickly destroyed it. That was a sobering video.
I have a Python, purchased recently. It's my first ship larger than an Asp Explorer. I literally hate losing a ship, take it personally. So, when I buy a ship, I work and save until I can buy everything on the ship A-rated. This makes a huge difference in survivability when encountering an enemy. I've taken out many interdictors, fought with a twin large beam lasered Vulture, and no one has ever touched my 250% military composite hull. The worst I've ever experienced is the Vulture taking 2 rings off my A-rated shields, which are fortified by 4 A-rated shield boosters. If an enemy can't take out your shields, you can't be hurt, so that is the first line of defense. But you can't afford to have A-rated shields without an A-rated power plant, and then an A-rated power distributor, and then... I think you'll get my point. When you go A-rated on anything, it quickly leads to A-rated almost everything.
Another thing that you may need to consider in a fight is good power distribution management. It matters a lot, depending on which stage of a fight you're in. Master this.
And last but not least, make one of the mottoes of the United States Marines, one of yours: "If you're engaged in a fair fight, you didn't properly prepare." Always choose your opponents carefully. Never engage in anything even close to a fair fight. When I'm interdicted, the first thing I do is boost away from my interdictor (here's where you need A-rated thrusters). I do this about 4 times, then chop the throttle to about 50%, deploy hard points, and nose up and over to face my opponent. I want to see what type of ship he/she is piloting. If I know it is a ship I can likely take, I will engage. If not, or if I'm not sure, I will boost past the my enemy and low wake out of there. Using this technigue, I recently saw that I had been interdicted by another Python, and most recently, an Anaconda. I fled to fight another day. Another time, I was mass locked by an interdictor. Knowing the mass lock scale for ships, I fled without bothering to turn around to see the pursuer.
I hope some of this helps. I've found my A-rated Python to be a formidable ship but not invulnerable. I use it primarily for hauling people, things, and information but it has an A-rated weapons loadout for those times I've had enough with the incessant NPC interdictions.
One last thing: Be very wary of squaring off against any human that performs an interdiction. Some of them are not pirates, merely space murderers. I lost an Adder to one who, instead of staying behind me, instantly climbed up to the right and behind me. That should have told me something was wrong. That player knew how to expose the maximum amount of my hull to his weapons and probably targeted my ship's power supply. 2 shots later, my ship was destroyed. Another time, I lost an Asp Explorer to a murderer using an engineer modified Pack Hound Missile setup. 2 shots, and my A-rated Asp Explorer was destroyed; I never stood a chance on that one.
When in doubt, flee. We all grind to hard for our credits to lose our valuable ships.
