Add ConfigurationError and base_hasattr

[jneeven]

No description provided.

[jneeven]

@AdamHillier I've only replaced the AttributeErrors, but there are many more errors that could be made ConfigurationErrors, for example things like

         raise ValueError(
                        "Setting already configured component field values directly is "
                        "prohibited. Use Zookeeper component configuration to set field "
                        "values."
                    )
            

[AdamHillier]

I really like having the ConfigurationError 👍

For base_hasattr, could you clarify the precise expected behaviour? Is the idea that it returns true if and only if name corresponds to a Field on the class OR hasattr(instance, name) returns true, in which case things like base_hasattr(instance, "__init__") will return true?

To be clear, I think this is useful functionality, I just want to be sure I fully understand the intention.

[jneeven]

For base_hasattr, could you clarify the precise expected behaviour? Is the idea that it returns true if and only if name corresponds to a Field on the class OR hasattr(instance, name) returns true, in which case things like base_hasattr(instance, "__init__") will return true?

Exactly, I've added a docstring. It's identical to hasattr, except that this does not throw any error when the attribute was not configured yet, and it returns True for unconfigured fields with allow_missing=True, which the normal hasattr does not.

[AdamHillier]

Nice :)