Sympy solve returns strange dictionary, when it should not return any

You can't access via dict_min[x] or dict_min["x"] because x is of type sympy.core.symbol.Symbol. The keys of this dict are of type sympy.core.symbol.Symbol.

dict_min[x] does not work because no x variable is defined in your code.

dict_min["x"] does not work because here you define x as a string, but the key named x in dict_min is of type sympy.core.symbol.Symbol.

There is no problem with your class.

However, you can do this:

dict_min[funz.x]

or:

x = funz.x
dict_min[x]

So, dict_min is not a strange dict type from sympy, that's a classic Python dict which keys are of type sympy.core.symbol.Symbol. The keys are the symbols of your equation. Perhaps it was confusing because your symbols x and y were defined in your class and via sym.symbols('x y').

If you want to ALWAYS get a list:

In minim, you should set dict=True instead of False. By doing this, you will "always get a list of solution mappings" (https://docs.sympy.org/latest/modules/solvers/solvers.html). Yes, the goal of dict=True is to ensure that the returned variable will be of type list . I agree that could seems a bit strange.

Some informations about this flag from the source code of solve(): https://github.com/sympy/sympy/blob/master/sympy/solvers/solvers.py#L406

And here is the effect of the flag is_dict: https://github.com/sympy/sympy/blob/master/sympy/solvers/solvers.py#L1249

As for sympy 1.9.