2. copy module

Status:in progress

The copy module implements shallow and deep copying operations.

2.1. How to copy a list

Three ways:

>>> l2 = list(l)
>>> l2 = l[:]
>>> import copy
>>> l2 = copy.copy(l)

Warning

Don’t do l2 = l, which is a reference, not a copy.

The preceding techniques for copying a list create shallow copies. IT means that nested objects will not be copied. Consider this example:

>>> a = [1, 2, [3, 4]]
>>> b = a[:]
>>> a[2][0] = 10
>>> a
[1, 2, [10, 4]]
>>> b
[1, 2, [10, 4]]

To get around this problem, you must perform a deep copy:

>>> import copy
>>> a = [1, 2, [3, 4]]
>>> b = copy.deppcopy(a)
>>> a[2][0] = 10
>>> a
[1, 2, [10, 4]]
>>> b
[1, 2, [3, 4]]