How to Rename a Dictionary Key in Python Without Reassignment or Iteration?

Renaming a Dictionary Key Without Reassignment or Iteration

When manipulating dictionaries, it may be necessary to rename a key without reassigning its value to a new name or iterating through the dictionary. This can be achieved using different methods depending on the type of dictionary being used.

For a regular Python dictionary, the following code snippet can be used:

<code class="python">mydict[k_new] = mydict.pop(k_old)</code>

This moves the item corresponding to the key to be renamed to the end of the dictionary, unless k_new already exists in the dictionary, in which case it overwrites the existing value with the value from the renamed key.

For a Python 3.7 OrderedDict where the ordering of keys needs to be preserved, a new instance of the dictionary needs to be created. For example, to rename key 2 to 'two':

<code class="python">d = {0:0, 1:1, 2:2, 3:3}
new_d = {
    "two" if k == 2 else k: v for k, v in d.items()
}</code>

The same approach can be applied to OrderedDicts, using a generator expression:

<code class="python">new_od = OrderedDict(
    (k_new if k == k_old else k, v) for k, v in od.items()
)</code>

It's worth noting that modifying the key itself, as the question suggests, is typically not feasible as keys in dictionaries are typically hashable and immutable.

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