Finding the Common items among Python dictionaries

A Dictionary is one of the unordered data structures available in python to store the data in the key and value pair. It is also known as Associative array or Hash map in other programming languages. The dictionary is represented using the curly braces {} and the key and value are separated using a colon “:” The keys in the dictionary are unique and the values can be of duplicates. To access the elements of the dictionary we will use the keys.

Example

The following is the example of creating a dictionary using the dic() method and curly braces {} available in python.

# creating dictionary using dict() method:
l = [('name', 'John'), ('age', 25), ('city', 'New York')]
dic = dict(l)
print("The dictionary created using dict() method",dic)
# creating dictionary using {}:
dic = {'name' : 'John', 'age' : 25, 'city' :'New York'}
print("The dictionary created using {}",dic)

Output

The dictionary created using dict() method {'name': 'John', 'age': 25, 'city': 'New York'}
The dictionary created using {} {'name': 'John', 'age': 25, 'city': 'New York'}

There are multiple approaches for finding the common items among python dictionaries. Let’s see each approach in detail.

Using Set Intersection

One straightforward approach is to convert the keys of the dictionaries into sets and then use the set intersection operation & to find the common keys.

Example

In this example, we first convert the keys of dict1 and dict2 into sets using set(dict1.keys()) and set(dict2.keys()). Then, set intersection & operator performs the set intersection, resulting in a set of common keys. Finally, we create a new dictionary, common_items, by iterating over the common keys and fetching the corresponding values from dict1.

dict1 = {'a': 1, 'b': 2, 'c': 3}
dict2 = {'b': 20, 'c': 30, 'd': 40}
common_keys = set(dict1.keys()) & set(dict2.keys())
common_items = {key: dict1[key] for key in common_keys}
print("The common items in the dictionaries dict1,dict2:",common_items)

Output

The common items in the dictionaries dict1,dict2: {'c': 3, 'b': 2}

Using Dictionary Comprehension

The approach is to use a dictionary comprehension which directly creates a new dictionary with only the common key-value pairs.

Example

In this approach, we iterate over the keys of dict1 using for key in dict1, and for each key, we check if it exists in dict2 using the condition if key in dict2. If the condition is true, we include the key-value pair in the common_items dictionary.

dict1 = {'a': 1, 'b': 2, 'c': 3}
dict2 = {'b': 20, 'c': 30, 'd': 40}
common_items = {key: dict1[key] for key in dict1 if key in dict2}
print("The common items in the dictionaries dict1,dict2:",common_items)

Output

The common items in the dictionaries dict1,dict2: {'b': 2, 'c': 3}

Using the items() Method

The items() method returns a view object that contains key-value pairs of the dictionary. We can use this method to iterate over the items and filter out the common items.

Example

In this approach, we use the items() method to iterate over the key-value pairs of dict1 using for key, value in dict1.items(). We then check if the key exists in dict2 and if the corresponding values in both dictionaries are the same. If these conditions are met, we include the key-value pair in the common_items dictionary.

dict1 = {'a': 1, 'b': 2, 'c': 3}
dict2 = {'b': 20, 'c': 30, 'd': 40}
common_items = {key: value for key, value in dict1.items() if key in dict2 and dict2[key] == value}
print("The common items in the dictionaries dict1,dict2:",common_items)

Output

The common items in the dictionaries dict1,dict2: {}