"class types.MappingProxyType(mapping) 
Read-only proxy of a mapping. ..."

is the only class in 7.11.2. Standard Interpreter Types that *does* have a signature given in the text. However, the extra word 'class' here and for SimpleNamespace confuses me (I do not understand what it is intended to convey) and seems unnecessary. The two entries with signatures in 7.11.1 do not have that.

Once parenthesized signatures are given, perhaps one statement at the top like "Classes listed without a signature cannot be directly created from Python code." would be sufficient.