Why does Python's copy.copy() return a object not equal to the original? -

in python, if copy list or dictionary, copied instance equal original:

>>> = [1, 2, 3] >>> b = copy.copy(a) >>> == b true >>> = {"a":1, "b":2} >>> b = copy.copy(a) >>> == b true 

but if copy object, result not equal original:

>>> class myclass(): ...     def __init__(self, name): ...             self._name= name ... >>> = myclass('a') >>> b = copy.copy(a) >>> == b false 

why?

equality in python objects checked calling __eq__() function.

example:

>>> class ca: ...     def __eq__(self, other): ...             print("equals") ...             return true ... >>> c = ca() >>> b = ca() >>> c == b equals true 

that because list equality dependent on elements , not actual memory location (reference) list stored, is, can 2 different list references, if have same elements in same order, lists equal.

example:

>>> l = [1,2] >>> l1 = [1,2] >>> id(l) 2830504 >>> id(l1) 2831864 >>> l == l1 true 

but custom class, have not overwritten __eq__(), hence call __eq__() of parent class, object, , checks equality based on reference.

and when copy.copy() shallow copying, is, creates new instance object members (attributes, etc.) remaining same. hence, unequal (as different references/different instances).

if want myclass check equality based on self._name, have overwrite __eq__() function that.

you can find more information comparisons here.