Merge Two Lists into a Dictionary in Python

In Python, lists and dictionaries are two common data structures. Lists are ordered collections that can contain data of any type, while dictionaries are unordered collections of key-value pairs, where each key corresponds to a value.

Sometimes, we need to merge two lists into a dictionary, where one list contains the keys and the other contains the corresponding values. This article will introduce several methods to achieve this.

Method 1: Using the zip Function

Python’s built-in zip function combines multiple iterables into a single iterator consisting of tuples. We can use it to merge two lists into a single list of tuples, which can then be converted to a dictionary.

keys = ['a', 'b', 'c']
values = [1, 2, 3]
dictionary = dict(zip(keys, values))
print(dictionary) # {'a': 1, 'b': 2, 'c': 3}

In the above code, we define two lists, keys and values, to store keys and values, respectively. We then use the zip function to combine them and convert the result into a dictionary.

Note that if the two lists are of different lengths, the zip function will only combine the shorter part; the remaining part will be ignored.

Method 2: Using Dictionary Comprehensions

In addition to using the zip function, we can also use dictionary comprehensions to combine two lists into a dictionary. Dictionary comprehensions are a quick way to create dictionaries, and their syntax is similar to list comprehensions.

keys = ['a', 'b', 'c']
values = [1, 2, 3]
dictionary = {keys[i]: values[i] for i in range(len(keys))}
print(dictionary) # {'a': 1, 'b': 2, 'c': 3}

In the above code, we use a for loop to iterate over the keys list and use it as the dictionary key. We also use the corresponding position of the value list element as the value, and then enclose it in curly braces to form a dictionary comprehension.

Method 3: Using the enumerate function

An even simpler method is to use the enumerate function to get the position of an element in a list and then include it in a dictionary along with the corresponding position of the element in another list.

keys = ['a', 'b', 'c']
values = [1, 2, 3]
dictionary = {keys[i]: value for i, value in enumerate(values)}
print(dictionary) # {'a': 1, 'b': 2, 'c': 3}

In the above code, we use a for loop and the enumerate function to iterate over the values list and use it as the dictionary value. We also use the corresponding element in the keys list as the key, and then enclose it in curly braces to form a dictionary comprehension.

Method 4: Using the dict.fromkeys Function

Finally, we can also use the fromkeys method of a dictionary to create a new dictionary where the value corresponding to each key is None. We can then use a for loop and slicing to replace the value of each key in the dictionary with the element at the corresponding position in the other list.

keys = ['a', 'b', 'c']
values = [1, 2, 3]
dictionary = dict.fromkeys(keys)
for i, key in enumerate(keys):
dictionary[key] = values[i]
print(dictionary) # {'a': 1, 'b': 2, 'c': 3}

In the above code, we first use the dictionary’s fromkeys method to create a new dictionary where each key has a value of None. Then, we use a for loop and slicing to replace the value of each key in the dictionary with the element at the corresponding position in the values list.

Conclusion

This article introduced four methods for merging two lists into a dictionary: using the zip function, dictionary comprehensions, the enumerate function, and the dict.fromkeys method. Each method is applicable in different situations, and you can choose the appropriate one based on your needs.

It is important to note that when using these methods, ensure that the order and number of elements in the two lists match correctly; otherwise, the results may not match your expectations.