Suppose i have a python list l consisting of immutables.When i am doing a shallow copy and a deep copy, the result is same:
>>> a = (1,2) # immutable types
>>> b = (3,4)
>>> l = [a,b] # a list containing immutable types
>>> import copy
>>> y = copy.copy(l) # shallow copy
>>> z = copy.deepcopy(l) # deep copy
>>> id(l[0])
139857440375584
>>> id(y[0])
139857440375584
>>> id(z[0])
139857440375584 # all have the same id's , so all refer to the same object
Does it means that shallow copy and deep copy has a meaning only for collections of mutable types because immutable types never changes. But if we want to achieve a deep copy like behavior for the these type of collections how can we do that?
Regards.
Since you cannot change the immutable objects, there is no point in creating copies of the same while copying.
As per copy's source code, shallow copy of immutable types is done like this
def _copy_immutable(x):
return x
for t in (type(None), int, long, float, bool, str, tuple,
frozenset, type, xrange, types.ClassType,
types.BuiltinFunctionType, type(Ellipsis),
types.FunctionType, weakref.ref):
d[t] = _copy_immutable
For all the immutable types, the _copy_immutable function returns the object as it is, during shallow copy.
The same way, during the deepcopy of tuples, the object is returned as is, as per the _deepcopy_tuple function,
d = id(x)
try:
return memo[d]
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