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.

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.

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

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

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)

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

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}

Other answers are pretty good.But in python3.6, regular dict also has order. So it's hard to keep key's position in normal case.

def rename(old_dict,old_name,new_name):
    new_dict = {}
    for key,value in zip(old_dict.keys(),old_dict.values()):
	    new_key = key if key != old_name else new_name
	    new_dict[new_key] = old_dict[key]
    return new_dict

In Python 3.6 (onwards?) I would go for the following one-liner

test = {'a': 1, 'old': 2, 'c': 3}
old_k = 'old'
new_k = 'new'
new_v = 4  # optional

print(dict((new_k, new_v) if k == old_k else (k, v) for k, v in test.items()))

which produces

{'a': 1, 'new': 4, 'c': 3}

May be worth noting that without the print statement the ipython console/jupyter notebook present the dictionary in an order of their choosing...

Suppose you want to rename key k3 to k4:

temp_dict = {'k1':'v1', 'k2':'v2', 'k3':'v3'}
temp_dict['k4']= temp_dict.pop('k3')

In case someone wants to rename all the keys at once providing a list with the new names:

def rename_keys(dict_, new_keys):
    """
     new_keys: type List(), must match length of dict_
    """

    # dict_ = {oldK: value}
    # d1={oldK:newK,} maps old keys to the new ones:  
    d1 = dict( zip( list(dict_.keys()), new_keys) )

          # d1{oldK} == new_key 
    return {d1[oldK]: value for oldK, value in dict_.items()}

I am using @wim 's answer above, with dict.pop() when renaming keys, but I found a gotcha. Cycling through the dict to change the keys, without separating the list of old keys completely from the dict instance, resulted in cycling new, changed keys into the loop, and missing some existing keys.

To start with, I did it this way:

for current_key in my_dict:
    new_key = current_key.replace(':','_')
    fixed_metadata[new_key] = fixed_metadata.pop(current_key)

I found that cycling through the dict in this way, the dictionary kept finding keys even when it shouldn't, i.e., the new keys, the ones I had changed! I needed to separate the instances completely from each other to (a) avoid finding my own changed keys in the for loop, and (b) find some keys that were not being found within the loop for some reason.

I am doing this now:

current_keys = list(my_dict.keys())
for current_key in current_keys:
    and so on...

Converting the my_dict.keys() to a list was necessary to get free of the reference to the changing dict. Just using my_dict.keys() kept me tied to the original instance, with the strange side effects.

@helloswift123 I like your function. Here is a modification to rename multiple keys in a single call:

def rename(d, keymap):
    """
    :param d: old dict
    :type d: dict
    :param keymap: [{:keys from-keys :values to-keys} keymap]
    :returns: new dict
    :rtype: dict
    """
    new_dict = {}
    for key, value in zip(d.keys(), d.values()):
        new_key = keymap.get(key, key)
        new_dict[new_key] = d[key]
    return new_dict

I came up with this function which does not mutate the original dictionary. This function also supports list of dictionaries too.

import functools
from typing import Union, Dict, List


def rename_dict_keys(
    data: Union[Dict, List[Dict]], old_key: str, new_key: str
):
    """
    This function renames dictionary keys

    :param data:
    :param old_key:
    :param new_key:
    :return: Union[Dict, List[Dict]]
    """
    if isinstance(data, dict):
        res = {k: v for k, v in data.items() if k != old_key}
        try:
            res[new_key] = data[old_key]
        except KeyError:
            raise KeyError(
                "cannot rename key as old key '%s' is not present in data"
                % old_key
            )
        return res
    elif isinstance(data, list):
        return list(
            map(
                functools.partial(
                    rename_dict_keys, old_key=old_key, new_key=new_key
                ),
                data,
            )
        )
    raise ValueError("expected type List[Dict] or Dict got '%s' for data" % type(data))

I have combined some answers from the above thread and come up with the solution below. Although it is simple it can be used as a building block for making more complex key updates from a dictionary.

test_dict = {'a': 1, 'b': 2, 'c': 3}
print(test_dict)
# {'a': 1, 'b': 2, 'c': 3}
prefix = 'up'
def dict_key_update(json_file):    
    new_keys = []
    old_keys = []
    for i,(key,value) in enumerate(json_file.items()):
        old_keys.append(key)
        new_keys.append(str(prefix) + key) # i have updated by adding a prefix to the 
        # key
    for old_key, new_key in zip(old_keys,new_keys):
        print('old {}, new {}'.format(old_key, new_key))
        if new_key!=old_key:  
           json_file[new_key] = json_file.pop(old_key)
     return json_file

test_dict = dict_key_update(test_dict)
print(test_dict)
# {'upa': 1, 'upb': 2, 'upc': 3}