Use cases and "how-to..."

...customize a subtype's text rendition

In a subclass, override _excl_from_repr, using key and/or type of value.

The most basic implementation is a no-op, excluding nothing:

def _excl_from_repr(self, k, cls):
    return False

To exclude by key, though, you can do something like:

def _excl_from_repr(self, k, cls):
    protected = ["reserved_metadata", "REZKEY"]
    return k in protected

To exclude by value type, you can use something like:

def _excl_from_repr(self, k, cls):
    return issubclass(cls, BaseOmissionType)

where BaseOmissionType is a proxy for the name of some type of values that may be stored in your mapping but that you prefer to not display in its text representation.

The two kinds of exclusion criteria may be combined as desired. Note that it's often advisable to invoke the superclass version of the method, but to achieve the intended effect this may be skipped.