Convert List to List of dictionaries in Python

Data handling or organizing or structuring in Python has a lot of common tasks and 1 such task is the conversion of list to list of dictionaries. It is a simple process that allows us to associate specific keys with their corresponding values; creating a collection of dictionaries that can be simply accessed and/or manipulated.

Before going forward with the techniques let us 1st see an example input and output. Consider the following:

Input

test_list = ['John', 25, 'Smith', 30, 'Alice', 35]
key_list = ['name', 'age']

Output

[{'name': 'John', 'age': 25}, {'name': 'Smith', 'age': 30}, {'name': 'Alice', 'age': 35}]

Method 1: Using a Loop

In this approach we simply take a list that contains alternating names and ages and convert it to a list of dictionaries wherein each resultant dictionary list represents a person’s info with keys for ‘name’ and ‘age’. By running a loop iteration over the original list and then grouping the values based upon the keys provided. The dictionaries created are appended to a list “result”.

Example

test_list = ['John', 25, 'Smith', 30, 'Alice', 35]
key_list = ['name', 'age']

result = []
for i in range(0, len(test_list), len(key_list)):
   temp_dict = {}
   for j, key in enumerate(key_list):
      temp_dict[key] = test_list[i + j]
   result.append(temp_dict)

print(result)

Output

[{'name': 'John', 'age': 25}, {'name': 'Smith', 'age': 30}, {'name': 'Alice', 'age': 35}]

Method 2: Using a List Comprehension with Zip()

This is another approach towards our goal and makes use of list comprehensions to convert list to list of dictionaries. It iterates over the test_list in chunks which is determined the length of the key_list thereby creating dictionaries which are paired with elements from key_list with their corresponding elements from the test_list slice. It then finally appends them to the result list which is a list of dictionaries. The zip() function is responsible for the pairing of elements.

Example

test_list = ['John', 25, 'Smith', 30, 'Alice', 35]
key_list = ['name', 'age']

result = [{key: value for key, value in zip(key_list, test_list[i:i+len(key_list)])} for i in range(0, len(test_list), len(key_list))]

print(result)

Output

[{'name': 'John', 'age': 25}, {'name': 'Smith', 'age': 30}, {'name': 'Alice', 'age': 35}]

Method 3: Using a List Comprehension with Slicing

This method also makes use of list comprehensions to iterate over the test_list (created at the start of the code) in increments of the length of the key_list. Inside of the list comprehension, we have a dictionary comprehension which creates dictionaries by pairing the keys from the key_list with the help of the values present in test_list using indexing.

Example

test_list = ['John', 25, 'Smith', 30, 'Alice', 35]
key_list = ['name', 'age']

result = [{key_list[j]: test_list[i+j] for j in range(len(key_list))} for i in range(0, len(test_list), len(key_list))]
print(result)

Output

[{'name': 'John', 'age': 25}, {'name': 'Smith', 'age': 30}, {'name': 'Alice', 'age': 35}]

Method 4: Using Itertools.islice() and Iter()

It is common in Python to use itertools for iterations. One of its functions, islice(), allows us to extract a specific portion of an iterable by specifying the starting and ending indices. By using iter(test_list), we can create an iterator for test_list. This iterator can then be used with islice() to extract a specific number of elements from the test_list.

The zip function combines the sliced elements with the key_list. Then, a dictionary comprehension is utilized to create dictionaries. It's important to note that the number of iterations in the code below is determined by a formula: length(test_list) divided by length(key_list).

Example

import itertools

test_list = ['John', 25, 'Smith', 30, 'Alice', 35]
key_list = ['name', 'age']

iter_test = iter(test_list)
result = [{key: value for key, value in zip(key_list, itertools.islice(iter_test, len(key_list)))} for _ in range(len(test_list) // len(key_list))]

print(result)

Output

[{'name': 'John', 'age': 25}, {'name': 'Smith', 'age': 30}, {'name': 'Alice', 'age': 35}]

Method 5: Using a Generator Function

Generator functions are a type of function that can generate a sequence of values and yields them 1 at a time; allowing for efficient memory usage. The yield keyword is used produce values and the function can be iterated over with the help of a simple loop. The below approach defines a generator known as generate_dicts which takes input as test_list and key_list. The dictionaries are generated by pairing elements form the key_list with their corresponding elements in the test_list.

Example

def generate_dicts(test_list, key_list):
   for i in range(0, len(test_list), len(key_list)):
      yield {key_list[j]: test_list[i+j] for j in 
# yield keyword instead of return
range(len(key_list))}

test_list = ['John', 25, 'Smith', 30, 'Alice', 35]
key_list = ['name', 'age']

result = list(generate_dicts(test_list, key_list))
print(result)

Output

[{'name': 'John', 'age': 25}, {'name': 'Smith', 'age': 30}, {'name': 'Alice', 'age': 35}]

Conclusion

In this article, we have discovered different methods to convert a list into a list of dictionaries in Python. These methods include using loops; list comprehensions with zip(); list comprehension with slicing; itertools.islice() and iter() and lastly generator functions . All these methods offer us flexibility for transforming data into structured format. All the methods have a linear time complexity of O(n).