copy - shallow and deep copy operations

Assignment statements in Python do not copy objects, they create bindings between a target and an object. For collections that are mutable or contain mutable items, a copy is sometimes needed so one can change one copy without changing the other. 

: Python에서 =(assignment) 연산자는 reference를 복사하지, object 자체를 복사하는 게 아니다. 

copy.copy(x)

Return a shallow copy of x.

copy.deepcopy(x)

Return a deep copy of x.

[ Shallow copy와 Deep copy의 차이점 ]

-> The difference between shallow and deep copying is only relevant for compound objects (objects that contain other objects like lists or class instances.).

-> A shallow copy constructs a new compound object and then (to the extent possible) inserts references into it to the objects found in the original.

-> A deep copy constructs a new compound object and then, recursively, inserts copies into it of the objects found in the original.

[ Deep copy가 가질 수 있는 문제점 ] 

-> Recursive objects (compound objects that, directly or indirectly, contain a reference to themselves) may cause a recursive loop.

-> Because deep copy copies everything it may copy too much, such as data which is intended to be shared between copies. 

[ Tip ]

 list 안의 element가 일반적인 int일 경우, copy.copy()의 shallow copy만으로 충분하다.