In this article we will discuss different ways to merge two or more dictionaries. Also, handle scenarios where we need to keep the values of common keys instead of overwriting them.

Merge two dictionaries using dict.update()

In Python, the Dictionary class provides a function update() i.e.

It accepts an another dictionary or an Iterable object (collection of key value pairs) as argument. Then merges the contents of this passed  dictionary or Iterable in the current dictionary.

Let’s use this update() function to merge two dictionaries.

Suppose we have two dictionaries i.e.

Both dictionaries has a common key ‘Sam’ with different values. Now let’s merge the contents of dict2 in dict1 i.e.

Now the content of dict1 is,

All the elements in dict2 are added to dict1. Keys which are common in both the dictionaries will contain the values as in dict2. Basically the dictionary we are passing in update() as argument will override the common key’s values. Therefore ‘Sam’ has value 20 now.

Another important point to notice is that, we didn’t got a new dictionary. The contents of dict1 changed and now apart from its existing contents it has the contents of dict2 too. What if we want to merged the contents of 2 or dictionaries to a new dictionary ? Let’s see how to do that.

Merge two or more Dictionaries using **kwargs

**kwargs

Using **kwargs we can send variable length key-value pairs to a function. When we apply ** to a dictionary, then it expands the contents in dictionary as a collection of key value pairs.
For example, if we have a dictionary i.e.

When we apply ** to this dictionary, it de-serializes the contents of dictionary to a collection of key/value pairs i.e.

is equivalent to,

So, let’s use **kwargs to merge two or more dictionaries.
Suppose we have two dictionaries i.e.

Now merge the contents of dict1 and dict2 to a new dictionary dict3 i.e.

Content of the new dictionary is,

How did it worked ?

**dict1 & **dict2 expanded the contents of both the dictionaries to a collection of key value pairs i.e.

Therefore, a new dictionary is created that contains the data from both the dictionaries.

Both dict1 & dict2 had one common key ‘Sam’. In dict3 value for this common key ‘Sam’ is as in dict2 because we passed the **dict2 as second argument.

Merge three dictionaries

Similarly we can merge 3 dictionaries i.e.

Output:

Till now we have seen that while merging dictionaries, values of common keys are getting overridden. What if we want to keep all the values ?

Merge two dictionaries and add values of common keys

Suppose we have two dictionaries with common key i.e.

Now we want to merge these dictionaries in way that it should keep all the values for common keys in a list i.e.

Output:

Both the dictionaries had a common key ‘Sam’. In the merged dictionary dict3, both the values of ‘Sam’ from dict1 & dict2 are merged to a list.

We can use this function to merge 3 dictionaries and keep the all the values for common keys i.e.

Output:

Complete example is as follows :

Output:

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