Python dictionaries are a powerful data structure that allows you to store data in key-value pairs. Merging two dictionaries is a common operation in Python, and there are several ways to achieve this. In this article, we will explore different methods to merge dictionaries in Python and provide detailed explanations along with code examples.
What is a Dictionary in Python?
A dictionary is an unordered collection of key-value pairs, where each key is unique. It allows you to access the values using their corresponding keys. Dictionaries are mutable, which means you can modify their contents after they are created.
Here's an example of a dictionary in Python:
Example:
sample_dict = { "Language_1": "Python", "Language_2": "C++", "Language_3": "Java" } print(sample_dict)
In the above example -
- The dictionary is called sample_dict.
- It contains three pairs of information, each with a "key" and a "value."
- The keys are "Language_1", "Langauge_2", and "Language_3".
- The corresponding values are "Python", "C++", and "Java".
Output:
{'Language_1': 'Python', 'Langauge_2': 'C++', 'Language_3': 'Java'}
Each key and its corresponding value are shown inside curly braces {}. This code helps store and access information in an organized way.
If you want to learn more about how to create and access dictionaries in Python, check out our detailed article on Python dictionaries.
Merging Dictionaries with a Basic Approach
Before we explore other methods, let's take a look at the simplest way to merge two dictionaries in python.
Apart from using built-in methods and operators, you can merge dictionaries manually by iterating over the key-value pairs of one dictionary and adding them to another.
Here's an example:
dict1 = {"a": 1, "b": 2} dict2 = {"c": 3, "d": 4} merged_dict = dict1.copy() for key, value in dict2.items(): merged_dict[key] = value print(merged_dict)
Output:
{"a": 1, "b": 2, "c": 3, "d": 4}
In the above example, we manually iterate over the key-value pairs of dict2 and add them to merged_dict. After the loop, merged_dict contains all the key-value pairs from both dictionaries. This method, while straightforward, can be a bit cumbersome for larger dictionaries, but it helps illustrate the basic concept of merging dictionaries in Python.
How to Merge Two Dictionaries in Python?
Below are the 8 unique methods by which you can concatenate two dictionaries in python:
1) Using update() method
You can merge two dictionaries in python using the update() method. Using the update method, the first dictionary is merged with the other one by overwriting it. Hence, no new dictionary is created, and it returns None. If both dictionaries contain the same key and different values, then the final output will overwrite the value of the latter dictionary.
Example:
dict_1 = {'John': 15, 'Rick': 10, 'Misa' : 12 } dict_2 = {'Bonnie': 18,'Rick': 20,'Matt' : 16 } dict_1.update(dict_2) print('Updated dictionary:') print(dict_1)
Output:
{'John': 15, 'Rick': 20, 'Misa': 12, 'Bonnie': 18, 'Matt': 16}
2) Using merge(|) operator
You can merge two dictionaries using the | operator. It is a very convenient method to merge dictionaries; however, it is only used in the Python 3.9 version or more.
Example:
def Merge(dict_1, dict_2): result = dict_1 | dict_2 return result # Driver code dict_1 = {'John': 15, 'Rick': 10, 'Misa' : 12 } dict_2 = {'Bonnie': 18,'Rick': 20,'Matt' : 16 } dict_3 = Merge(dict_1, dict_2) print(dict_3)
Output:
{'John': 15, 'Rick': 20, 'Misa': 12, 'Bonnie': 18, 'Matt': 16}
3) Using ** operator
The simplest way to concatenate two dictionaries in Python is by using the unpacking operator(**). By applying the "**" operator to the dictionary, it expands its content being the collection of key-value pairs.
For example, if you apply "**" to dict_1 as shown below, the output will collect key-value pairs stored inside dict_1.
Example:
dict_1 = {'John': 15, 'Rick': 10, 'Misa': 12} print(dict(**dict_1))
Output:
{'John': 15, 'Rick': 10, 'Misa': 12}
Now, to combine two dictionaries using "**", we will make use of an additional dictionary to store the final output. The content of dict_1 and dict_2 will expand using the "**" operator and combine to form dict_3.
Similar to the update method, if both dictionaries has the same key with different values, then the final output will contain the value of the second dictionary. Take a look at the below example for understanding the working of the "**" operator.
Example:
dict_1 = {'John': 15, 'Rick': 10, 'Misa' : 12 } dict_2 = {'Bonnie': 18,'Rick': 20,'Matt' : 16 } dict_3 = {**dict_1,**dict_2} print(dict_3)
Output:
{'John': 15, 'Rick': 20, 'Misa': 12, 'Bonnie': 18, 'Matt': 16}
You can also merge three dictionaries at the same time using the “**” operator, as shown in the below example.
Example:
dict_1 = {'John': 15, 'Rick': 10, 'Misa' : 12 } dict_2 = {'Bonnie': 18,'Rick': 20,'Matt' : 16 } dict_3 = {'Stefan': 19, 'Riya': 14, 'Lora': 17} dict_4 = {**dict_1,**dict_2, **dict_3} print (dict_4)
Output:
{'John': 15, 'Rick': 20, 'Misa': 12, 'Bonnie': 18, 'Matt': 16, 'Stefan': 19, 'Riya': 14, 'Lora': 17}
4) Unpacking the second dictionary
Unpacking the second dictionary using the "**" operator will help you merge two dictionaries and get your final output. However, this method is not highly used and recommended because it will only work if the keys of the second dictionary are compulsorily strings. If any int value is encountered, then it will raise the "TypeError" method.
Example:
dict_1={'John': 15, 'Rick': 10, 'Misa' : 12 } dict_2={'Bonnie': 18,'Rick': 20,'Matt' : 16 } dict_3=dict(dict_1,**dict_2) print (dict_3)
Output:
{'John': 15, 'Rick': 20, 'Misa': 12, 'Bonnie': 18, 'Matt': 16}
5) Using collection.ChainMap() method
This is one of the least known methods to merge two dictionaries in python. Using collection.ChainMap() method, you have to make use of the collection module from the ChainMap library which will help you to group multiple dictionaries in a single view.
If both dictionaries contain the same key/s, then the value of the first dictionary is fetched in the final output. Note that we will make use of the “import..from..” syntax to import the collection module as shown in the below example:
Example:
from collections import ChainMap dict_1={'John': 15, 'Rick': 10, 'Misa' : 12 } dict_2={'Bonnie': 18,'Rick': 20,'Matt' : 16 } dict_3 = ChainMap(dict_1, dict_2) print(dict_3) print(dict(dict_3))
Output:
ChainMap({'John': 15, 'Rick': 10, 'Misa': 12}, {'Bonnie': 18, 'Rick': 20, 'Matt': 16})
{'Bonnie': 18, 'Rick': 10, 'Matt': 16, 'John': 15, 'Misa': 12}
6) Using itertools.chain()
The iterator returns the element from the first iterable until it's empty and then jumps to the next iterable. Basically, it will handle the consecutive sequence as a single sequence.
As the dictionary is also iterable, we can use the chain() function from itertools class and merge two dictionaries. The return type of this method will be an object, and hence, we can convert the dictionary using the dict() constructor.
Example:
import itertools dict_1={'John': 15, 'Rick': 10, 'Misa': 12} dict_2={'Bonnie': 18, 'Rick': 20, 'Matt': 16} dict_3=itertools.chain(dict_1.items(),dict_2.items()) #Returns an iterator object print (dict_3) print(dict(dict_3))
Output:
<itertools.chain object at 0x000001EB8E312520> {'John': 15, 'Rick': 20, 'Misa': 12, 'Bonnie': 18, 'Matt': 16}
7) Using dictionary comprehension
We can combine two dictionaries in python using dictionary comprehension. Here, we also use the for loop to iterate through the dictionary items and merge them to get the final output. If both dictionaries have common keys, then the final output using this method will contain the value of the second dictionary.
Example:
dict_1={'John': 15, 'Rick': 10, 'Misa': 12} dict_2={'Bonnie': 18, 'Rick': 20, 'Matt': 16} dict_3={k:v for d in (dict_1,dict_2) for k,v in d.items()} print (dict_3)
Output:
{'John': 15, 'Rick': 20, 'Misa': 12, 'Bonnie': 18, 'Matt': 16}
8) Add values of common keys
In all of the above methods, if both the dictionary contains the different data values of the same keys, the values in the final output were getting overridden. What if you wish to preserve all the value in the final output? For this purpose, you can merge the dictionaries such that it adds the values of the common keys in the list and return the final output.
In this method, we will also make use of for loop to traverse through the keys and values in the dictionary inside the function. Later, we will call the function to get the final output as merged dictionaries as shown below:
Example:
dict_1 = {'John': 15, 'Rick': 10, 'Misa': 12} dict_2 = {'Bonnie': 18, 'Rick': 20, 'Matt': 16} def mergeDictionary(dict_1, dict_2): dict_3 = {**dict_1, **dict_2} for key, value in dict_3.items(): if key in dict_1 and key in dict_2: dict_3[key] = [value , dict_1[key]] return dict_3 dict_3 = mergeDictionary(dict_1, dict_2) print(dict_3)
Output:
{'John': 15, 'Rick': [20, 10], 'Misa': 12, 'Bonnie': 18, 'Matt': 16}
Conclusion
In this article, we explored different methods to merge dictionaries in Python. We covered the update() method, the double asterisk operator (**), the chain() method, the ChainMap() method, and the merge operator (|). Each method has its own advantages and use cases, so choose the one that suits your needs. By using these methods, you can easily merge dictionaries and manipulate your data efficiently in Python.
Still, if you face any difficulty, get in touch with our Live python tutors to clear your doubts.
