I can't find a clear explanation of "immediate mode" GUI creation (which this library enables) but it appears to be the sort of paradigm that pre-dated object-oriented and event-driven interaction handling that became the norm in the mid 90s (especially after the popularising of dev tools from Borland and Microsoft eg. Visual Basic etc), so I guess it is a formalisation of the procedural (?) methods from the era prec…
This library has functions such as add_button() that can be used to create a hierarchy of widgets. From this, I suspect that the library is not fully operating in immediate mode, but perhaps it uses some kind of mixed mode?
From the linked readme: “DearPyGui provides a wrapping of DearImGui that provides a hybrid of a traditional retained mode GUI and Dear ImGui's immediate mode paradigm.”