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Python merge dictionaries with dicts as values how to#
Python merge dictionaries with dicts as values code#

Among other features, ChainMap objects are coupled to their underlying dictionaries and they handle removing items in an interesting way. There are two different scenarios to perform this task.

Python merge dictionaries with dicts as values code#

We may be okay with this if our code practices duck typing, but we’ll need to inspect the features of ChainMap to be sure. While working on dictionaries we may need to merge two dictionaries to obtain the resultant dictionary. Does this actually give us a dictionary?Ī ChainMap object is not a dictionary but it is a dictionary-like mapping. Changes to ChainMap objects affect the first dictionary provided and we don’t want user to change so we provided an empty dictionary first. Why is there an empty dictionary before user? The dictionaries are searched in order, so user returns matches before defaults. We ordered our arguments this way to ensure requirement 1 was met. > user =, user, defaults )Ī ChainMap groups dictionaries together into a proxy object (a “view”) lookups query each provided dictionary until a match is found. And also, concatenates the values with the same set of keys in the dictionary collection and adds all the lists in the same dictionary with the same key.

For concerns about mutability of nested objects, we should look into epcopy. Note: In 5, we’re focused on updates to the dictionary, not contained objects.

updates made to context should never alter defaults or user.

defaults and user should not change during the creation of context.

the values in defaults and user can be anything.

keys in defaults and user may be any valid keys.

user values should override defaults values in cases of duplicate keys In the latest release of Python 3.9.0a4, we can use the merging operator to merge two dicts very conveniently.

We want to combine these two dictionaries into a new dictionary called context. Our code has two dictionaries: user and defaults.

Our Problemīefore we can discuss solutions, we need to clearly define our problem.

Python merge dictionaries with dicts as values how to#

Let’s walk through the different ways of solving this problem and discuss which is the most Pythonic. How to Merge Two Dictionaries in Python Using the Double Asterisk Operator ( ) You can use the double asterisk (also called double star) operator ( ) to 'unpack' and merge the key and value pairs of two or more dictionaries into a variable. There are multiple ways to solve this problem: some are awkward, some are inaccurate, and most require multiple lines of code. Have you ever wanted to combine two or more dictionaries in Python?