Cloning a Dictionary

As we saw in the cloning lists section, if we code something like list_b = list_a, we create two variables that point to the SAME memory location. The same list has two different names. Anything we do to list_a also happens to list_b, since the two labels refer to the same set of data.

We call giving two names to the same data aliasing, and this can happen with dictionaries as well.

Example

opposites = {'up' : 'down', 'right' : 'wrong', 'hot' : 'cold'}
other = opposites

opposites['right'] = 'left'
print(opposites)
print(other)

Console Output

{'up' : 'down', 'right' : 'left', 'hot' : 'cold'}
{'up' : 'down', 'right' : 'left', 'hot' : 'cold'}

When we perform an action on the opposites dictionary, we see the effects when we use the other alias.

Create an Independent Copy

If we want to modify a dictionary but keep the original intact, we use the copy() method. The general syntax is:

dict_copy = original_dict.copy()

The copy() method creates a new dictionary in a new memory location and assigns it to the dict_copy variable. Changes made to the original dictionary will NOT affect the copy, and vice versa.

Example

opposites = {'up' : 'down', 'right' : 'wrong', 'hot' : 'cold'}
other = opposites.copy()

opposites['right'] = 'left'
other.pop('up')
print(opposites)
print(other)

Console Output

{'up' : 'down', 'right' : 'left', 'hot' : 'cold'}
{'right' : 'wrong', 'hot' : 'cold'}