@hauntsaninja I tried that but it didn’t work either:
error: Argument 1 to "replace" of "DateTime" has incompatible type "SupportsIndex | None"; expected "SupportsIndex" [arg-type]
I’m actually a little puzzled by how the type annotations in Typeshed are supposed to express “optional” 
@MegaIng thank you, that’s good to know! Does that include “optionality” of an argument?