The copy Module
As discussed in Chapter 4, assignment in Python does not copy the
right-hand side object being assigned. Rather, assignment adds a
reference to the right-hand side object. When you want a copy of
object x, you can ask
x for a copy of itself. If
x is a list,
x
[:] is a copy of
x. If x is a
dictionary, x
.copy( )
returns a copy of x.
The copy module supplies a copy
function that creates and returns a copy of most types of objects.
Normal copies, such as
x
[:] for a list
x and
copy.copy(
x
),
are also known as shallow copies. When x
has references to other objects (e.g., items or attributes), a normal
copy of x has distinct references to the
same objects. Sometimes, however, you need a deep copy, where
referenced objects are copied recursively. Module
copy supplies a
deepcopy(
x
)
function that performs a deep copy and returns it as the
function’s result.
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