How I can use eval to made class definitions inside other class ?
evalstr = str("class MyScreen(Screen):\n\tpass\n") eval(evalstr)
I want to execute this code in other class method. But it returns an error.
eval here (security concerns aside)
evalstr = str("class MyScreen(Screen):\n\tpass\n") exec(evalstr)
eval will only evaluate an expression and return it's value.
exec is used for executing arbitrary code strings as statements, which is what you need here.
But seriously this is a security disaster waiting to happen in most cases, consider alternatives (like writing the code not as a string).
EDIT: Chepner's answer is probably the right way to go.