Feature requests for Systems Framework Python bindings

[EricCousineau-TRI]

This issue will be a high-level track for Systems Framework Python bindings. Some of these features may be addressed by other people; if not specified, assume that I am responsible for them.

Current features (not ranked in any particular order)

• (pydrake: Use transitive py::keep_alive to aid in REPL-friendly behavior. #7742) REPL-friendly referencing, per @rdeits's request. Present limitations shown here. Options:
  1. Use py::keep_alive<> (which may drag around extra containers, and would be hard to denote transfers, like from DiagramBuilder --> DiagramBuilder::Build() --> Diagram)
  2. Use shared_ptr in Systems framework API. May have performance concerns (@sherm1), and would lock users into shared_ptr rather than unique_ptr for tracking internally.
• AbstractValues, unrestricted updates
• Discrete updates, events, etc.
• Scalar-type conversion. Would most likely use the prototype from Spike test extent to which Python can use the existing System framework #7185 (doesn't seem like too much of a technical challenge).
  • Updated prototype (2017/12/29): scalar_type_test.py
• RigidBodyPlant, per Russ's request.
• PoseVector (rendering_py: Add PoseVector. Enable by-value casting for geometric arguments. #7948), PoseBundle (Add initial pydrake bindings for maliput #8091)

EDIT: Moved upstreaming item to #5842. Moved binder item to #7889.
EDIT 2: Removed automotive_simulator to #7918.

[EricCousineau-TRI]

Update: Tracking dtype stuff in #8116; scalar type conversion was supported in #8701, with the caveat of no reference semantics.

Closing this issue.