Create a Dictionary with List Comprehension in Python

By using the dict() method in Python, we can create a dictionary with the list comprehension. Following is the syntax of dict() method-

dict(**kwarg)

Keyword arguments. We can pass one or more keyword arguments. If no keyword argument is passed, then the dict() method will create an empty dictionary object. The syntax for creating a dictionary with list comprehension:

dict(list_comprehension)

Creating Dictionary using List Comprehension

Instead of sending a number of keywords here, we need to send a list of tuples with key-value pairs to the dict() method. Let's take an example and create a dictionary using a list comprehension.

Example

To iterate over the for loop in list comprehension, we used the range() method. And also we used another Python built-in function, chr(), to get the string representation of the Unicode integers. In the output dictionary, the keys are created by the string representation of Unicode integers, and the values are created by a loop over integers -

dict_= dict([(chr(i), i) for i in range(100, 105)])
print('Output dictionary: ', dict_)
print(type(dict_))

Following is an output of the above code -

Output dictionary:  {'d': 100, 'e': 101, 'f': 102, 'g': 103, 'h': 104}
<class 'dict'>

Example

Here we have passed the two input lists, "data1" and "data2," to the list_comprehension using the zip() method. This zip() method creates an iterator based on 2 inputs, and finally the dictionary is created by using the list compression.

data1 = [1, 2, 3, 4, 5]
data2 = [10, 20, 30, 40, 50]
print('input list1: ', data1)
print('input list12: ', data2)

# create a dict using list comprehension
d = dict([(key, value) for key, value in zip(data1,data2)])
print('Output dictionary: ', d)
print(type(d))

Following is an output of the above code ?

input list1:  [1, 2, 3, 4, 5]
input list12:  [10, 20, 30, 40, 50]
Output dictionary:  {1: 10, 2: 20, 3: 30, 4: 40, 5: 50}
<class 'dict'>

Example

In the following example using the Python list comprehension technique, we have created a list of tuples, and each tuple has 2 elements. These two elements are then converted as keys and values to the dictionary object.

l = [( i,i*2) for i in range(1,10)]
print("Comprehension output:",l)

dict_= dict(l)
print('Output dictionary: ', dict_)
print(type(dict_))

Following is an output of the above code ?

Comprehension output: [(1, 2), (2, 4), (3, 6), (4, 8), (5, 10), (6, 12), (7, 14), (8, 16), (9, 18)]
Output dictionary:  {1: 2, 2: 4, 3: 6, 4: 8, 5: 10, 6: 12, 7: 14, 8: 16, 9: 18}
<class 'dict'>

Example

Finally, let's take another example and see how to create a dictionary with list comprehension in Python -

l = [20, 21, 65, 29, 76, 98, 35]
print('Input list: ', l)

# create a dict using list comprehension
d = dict([(val/2, val) for val in l])
print('Output dictionary: ', d)
print(type(d))

Following is an output of the above code ?

Input list:  [20, 21, 65, 29, 76, 98, 35]
Output dictionary:  {10.0: 20, 10.5: 21, 32.5: 65, 14.5: 29, 38.0: 76, 49.0: 98, 17.5: 35}
<class 'dict'>