dynamic typing is everywhere of courseyou don' really need to draw name/object diagrams with circles and arrows to use python when you're starting outthoughit sometimes helps you understand unusual cases if you can trace their reference structures as we've done here if mutable object changes out from under you when passed around your programfor examplechances are you are witnessing some of this subject matter firsthand moreovereven if dynamic typing seems little abstract at this pointyou probably will care about it eventually because everything seems to work by assignment and references in pythona basic understanding of this model is useful in many different contexts as you'll seeit works the same in assignment statementsfunction argumentsfor loop variablesmodule importsclass attributesand more the good news is that there is just one assignment model in pythononce you get handle on dynamic typingyou'll find that it works the same everywhere in the language at the most practical leveldynamic typing means there is less code for you to write just as importantlythoughdynamic typing is also the root of python' polymorphisma concept we introduced in and will revisit again later in this book because we do not constrain types in python codeit is both concise and highly flexible as you'll seewhen used welldynamic typing--and the polymorphism it implies-produces code that automatically adapts to new requirements as your systems evolve "weakreferences you may occasionally see the term "weak referencein the python world this is somewhat advanced toolbut is related to the reference model we've explored hereand like the is operatorcan' really be understood without it in shorta weak referenceimplemented by the weakref standard library moduleis reference to an object that does not by itself prevent the referenced object from being garbage-collected if the last remaining references to an object are weak referencesthe object is reclaimed and the weak references to it are automatically deleted (or otherwise notifiedthis can be useful in dictionary-based caches of large objectsfor exampleotherwisethe cache' reference alone would keep the object in memory indefinitely stillthis is really just special-case extension to the reference model for more detailssee python' library manual dynamic typing is everywhere