Python’s default implementation of deepcopy has several features that
are slower than they need to be. This is an implementation of
deepcopy that provides special handling to circumvent some of the
slowest parts of deepcopy().
Note
This implementation is not as aggressive about keeping the copied
state alive until the end of the deepcopy operation. In particular,
the dict, list and tuple handlers do not register their
source objects with the memo. This is acceptable, as
fast_deepcopy() is only called in situations where we are ensuring
that the source object will persist:
AutoSlots.__deepcopy_state__() explicitly preserved the
source state
Component.__deepcopy_field__() is only called by
AutoSlots.__deepcopy_state__() -
IndexedComponent._create_objects_for_deepcopy() is
deepcopying the raw keys from the source _data dict (which is
not a temporary object and will persist)
If other consumers wish to make use of this function (e.g., within
their implementation of __deepcopy__), they must remember that
they are responsible to ensure that any temporary source obj
persists.