Which objects are expanded by double-star ** operator?

[Terry Reedy]

The answer depends on the version:
in 2.5 "If the syntax "**expression" appears in the function call, 
"expression" must evaluate to a (subclass of) dictionary, "
in 3.1 "If the syntax **expression  appears in the function call, 
expression must evaluate to a mapping,"

ReferenceManual.Epressions.Primaries.Calls

Terry Jan Reedy