code is cluttered by try-except in Python

Does that help There is no "correct" answer for this, it's really a matter of priorities?
Does the code work? How well does it work? Are there deadlines? Is release more important than quality?

I hope this helps you . Have a look at the ContractClass and ContractClassFor attributes. This allows you to write classes with the code contracts in separate assemblies. This allows you to have the contracts available for dev work, doesn't clutter your code and also means you don't have to deploy the contracts with the live code:
Contract Class Attribute

I wish this helpful for you Input validation is always a good idea - the earlier this is done, the better. I recommend doing that for all non-private methods. Some people advocate doing this even for private methods too, just in case visibility is changed at any point. Others trust their own package and only validate public and protected methods.
There should be no need to perform validation in a getter. You have full control over the contents of your class, so your fields should not enter a bad state. The input validation ensures you are never setting state values that you don't later approve of in a getter. Remember defensive copying when you return mutable objects from a getter.

wish helps you Your condition basically breaks down into two pieces:
some set of variables are all zero some set of variables are all nonzero

should_be_zero = [b, d, e, f]
should_be_nonzero = [a, c]

all(i == 0 for i in should_be_zero) and all(i != 0 for i in should_be_nonzero)

not any(should_be_zero) and all(should_be_nonzero)