Dictionary to lowercase in Python

You will need to use either a loop or a list/generator comprehension. If you want to lowercase all the keys and values, you can do this::

dict((k.lower(), v.lower()) for k,v in {'My Key':'My Value'}.iteritems())

If you want to lowercase just the keys, you can do this::

dict((k.lower(), v) for k,v in {'My Key':'My Value'}.iteritems())

Generator expressions (used above) are often useful in building dictionaries; I use them all the time. All the expressivity of a loop comprehension with none of the memory overhead.

The following is identical to Rick Copeland's answer, just written without a using generator expression:

outdict = {}
for k, v in {'My Key': 'My Value'}.iteritems():
    outdict[k.lower()] = v.lower()

Generator-expressions, list comprehension's and (in Python 2.7 and higher) dict comprehension's are basically ways of rewriting loops.

In Python 2.7+, you can use a dictionary comprehension (it's a single line of code, but you can reformat them to make it more readable):

{k.lower():v.lower()
    for k, v in
    {'My Key': 'My Value'}.items()
}

They are quite often tidier than the loop equivalent, as you don't have to initialise an empty dict/list/etc.. but, if you need to do anything more than a single function/method call they can quickly become messy.

This will lowercase all your dict keys. Even if you have nested dict or lists. You can do something similar to apply other transformations.

def lowercase_keys(obj):
  if isinstance(obj, dict):
    obj = {key.lower(): value for key, value in obj.items()}
    for key, value in obj.items():         
      if isinstance(value, list):
        for idx, item in enumerate(value):
          value[idx] = lowercase_keys(item)
      obj[key] = lowercase_keys(value)
  return obj 

json_str = {"FOO": "BAR", "BAR": 123, "EMB_LIST": [{"FOO": "bar", "Bar": 123}, {"FOO": "bar", "Bar": 123}], "EMB_DICT": {"FOO": "BAR", "BAR": 123, "EMB_LIST": [{"FOO": "bar", "Bar": 123}, {"FOO": "bar", "Bar": 123}]}}

lowercase_keys(json_str)


Out[0]: {'foo': 'BAR',
 'bar': 123,
 'emb_list': [{'foo': 'bar', 'bar': 123}, {'foo': 'bar', 'bar': 123}],
 'emb_dict': {'foo': 'BAR',
  'bar': 123,
  'emb_list': [{'foo': 'bar', 'bar': 123}, {'foo': 'bar', 'bar': 123}]}}

I used JSON library to deserialize the dictionary first, apply lower case than convert back to dictionary

import json
mydict = {'UPPERCASE': 'camelValue'}
print(mydict)
mydict_in_str = json.dumps(mydict)
mydict_lowercase = json.loads(mydict_in_str.lower())
print(mydict_lowercase)

In Python 3:

d = dict()
d = {k.casefold(): v for k, v in d.items()}

In Python 3 you can do:

dict((k.lower(), v.lower()) for k,v in {'Key':'Value'}.items())

In Python 2 just substitute .items() for .iteritems():

dict((k.lower(), v.lower()) for k,v in {'Key':'Value'}.iteritems())