Rename a dictionary key

Is there a way to rename a dictionary key, without reassigning its value to a new name and removing the old name key; and without iterating through dict key/value?

In case of OrderedDict, do the same, while keeping that key's position.

Solution 1:

For a regular dict, you can use:

mydict[k_new] = mydict.pop(k_old)

This will move the item to the end of the dict, unless k_new was already existing in which case it will overwrite the value in-place.

For a Python 3.7+ dict where you additionally want to preserve the ordering, the simplest is to rebuild an entirely new instance. For example, renaming key 2 to 'two':

>>> d = {0:0, 1:1, 2:2, 3:3}
>>> {"two" if k == 2 else k:v for k,v in d.items()}
{0: 0, 1: 1, 'two': 2, 3: 3}

The same is true for an OrderedDict, where you can't use dict comprehension syntax, but you can use a generator expression:

OrderedDict((k_new if k == k_old else k, v) for k, v in od.items())

Modifying the key itself, as the question asks for, is impractical because keys are hashable which usually implies they're immutable and can't be modified.

Solution 2:

Using a check for newkey!=oldkey, this way you can do:

if newkey!=oldkey:  
    dictionary[newkey] = dictionary[oldkey]
    del dictionary[oldkey]

Solution 3:

In case of renaming all dictionary keys:

target_dict = {'k1':'v1', 'k2':'v2', 'k3':'v3'}
new_keys = ['k4','k5','k6']

for key,n_key in zip(target_dict.keys(), new_keys):
    target_dict[n_key] = target_dict.pop(key)

Solution 4:

You can use this OrderedDict recipe written by Raymond Hettinger and modify it to add a rename method, but this is going to be a O(N) in complexity:

def rename(self,key,new_key):
    ind = self._keys.index(key)  #get the index of old key, O(N) operation
    self._keys[ind] = new_key    #replace old key with new key in self._keys
    self[new_key] = self[key]    #add the new key, this is added at the end of self._keys
    self._keys.pop(-1)           #pop the last item in self._keys

Example:

dic = OrderedDict((("a",1),("b",2),("c",3)))
print dic
dic.rename("a","foo")
dic.rename("b","bar")
dic["d"] = 5
dic.rename("d","spam")
for k,v in  dic.items():
    print k,v

output:

OrderedDict({'a': 1, 'b': 2, 'c': 3})
foo 1
bar 2
c 3
spam 5

Solution 5:

A few people before me mentioned the .pop trick to delete and create a key in a one-liner.

I personally find the more explicit implementation more readable:

d = {'a': 1, 'b': 2}
v = d['b']
del d['b']
d['c'] = v

The code above returns {'a': 1, 'c': 2}