`traitlets.traitlets:link`

Signature

   class     link (    source  :  t.Any    ,    target  :  t.Any    ,    transform  :  t.Iterable[FuncT] | None    =  None     )   →  None

Link traits from different objects together so they remain in sync.

source : (object / attribute name) pair
target : (object / attribute name) pair
transform: iterable with two callables (optional): Data transformation between source and target and target and source.

class X(HasTraits):
    value = Int()

src = X(value=1)
tgt = X(value=42)
c = link((src, "value"), (tgt, "value"))

Setting source updates target objects:

src.value = 5
tgt.value