How to convert Python dictionary keys/values to lowercase?

A dictionary in Python is a collection of key-value pairs where each key is unique and maps to a specific value. Sometimes you need to convert dictionary keys or values to lowercase for consistency or comparison purposes.

Converting Both Keys and Values to Lowercase

To convert both dictionary keys and values to lowercase, you can use dictionary comprehension with the lower() method ?

def lower_dict(d):
    new_dict = dict((k.lower(), v.lower()) for k, v in d.items())
    return new_dict

original = {'Foo': "Hello", 'Bar': "World"}
result = lower_dict(original)
print(result)

{'foo': 'hello', 'bar': 'world'}

Converting Only Keys to Lowercase

When you need to convert only the keys to lowercase while keeping values unchanged ?

def lower_keys(d):
    new_dict = dict((k.lower(), v) for k, v in d.items())
    return new_dict

original = {'Foo': "Hello", 'Bar': "World"}
result = lower_keys(original)
print(result)

{'foo': 'Hello', 'bar': 'World'}

Using Dictionary Comprehension

Dictionary comprehension provides a more concise way to convert keys to lowercase ?

original_dict = {'Name': 'sai', 'AGE': 25, 'coUNTry': 'America'}
new_dict = {key.lower(): value for key, value in original_dict.items()}
print(new_dict)

{'name': 'sai', 'age': 25, 'country': 'America'}

Converting Only Values to Lowercase

To convert only string values to lowercase while preserving keys ?

original = {'Name': 'ALICE', 'City': 'NEW YORK', 'Age': 30}
new_dict = {key: value.lower() if isinstance(value, str) else value 
            for key, value in original.items()}
print(new_dict)

{'Name': 'alice', 'City': 'new york', 'Age': 30}

Comparison of Methods

Conclusion

Use dictionary comprehension for converting dictionary keys to lowercase as it's the most readable approach. When dealing with mixed data types, check with isinstance() to avoid errors on non-string values.