5 Best Ways to Convert Python Dict Keys to Int

💡 Problem Formulation: When manipulating dictionaries in Python, it may be necessary to transform the keys from strings to integers or other types, especially when dealing with JSON data or coming from other data sources. For example, if we have a dictionary {"1": "apple", "2": "banana"}, we may need to convert it to {1: "apple", 2: "banana"} for various computation purposes. This article explores different solutions to this conversion problem.

Method 1: Using a Dictionary Comprehension

A dictionary comprehension offers a concise and readable way to create a new dictionary from an existing one while converting the keys to integers. It iteratively goes over the items in the old dictionary and produces a new pair with the key cast to an int and the corresponding value.

Here’s an example:

original_dict = {"1": "apple", "2": "banana"}
converted_dict = {int(key): value for key, value in original_dict.items()}

Output:

{1: "apple", 2: "banana"}

This code snippet takes the key-value pairs in the original dictionary and uses a dictionary comprehension to cast the key to an int type. It creates a new dictionary converted_dict with integer keys and the same values.

Method 2: Using the map() Function

The map() function can be applied to the keys of a dictionary to convert them to integers, paired with a dict() constructor to produce the new dictionary with int keys.

Here’s an example:

original_dict = {"1": "apple", "2": "banana"}
converted_dict = dict(map(lambda kv: (int(kv[0]), kv[1]), original_dict.items()))

Output:

{1: "apple", 2: "banana"}

This snippet uses the map() function with a lambda that takes each key-value tuple and converts the key to int. The dict() constructor is then used to turn the map object into a dictionary.

Method 3: Using a For Loop

A traditional for loop can be used to iterate over the items in a dictionary, converting each key to an int, and inserting the new key-value pair into a new dictionary.

Here’s an example:

original_dict = {"1": "apple", "2": "banana"}
converted_dict = {}
for key, value in original_dict.items():
    converted_dict[int(key)] = value

Output:

{1: "apple", 2: "banana"}

This code uses a for loop to iterate through each key-value pair in the original dictionary. It converts each key to an integer with int(key) and assigns the corresponding value to the new key in converted_dict.

Method 4: Using JSON Parsing

When dealing with keys that are valid integers in a JSON string, we can parse the JSON using the json.loads() function with a custom object hook or decoder to convert the keys to integers during the parsing process.

Here’s an example:

import json
original_dict = '{"1": "apple", "2": "banana"}'

def int_keys_decoder(pairs):
    return {int(k): v for k, v in pairs}

converted_dict = json.loads(original_dict, object_pairs_hook=int_keys_decoder)

Output:

{1: "apple", 2: "banana"}

This snippet defines a function int_keys_decoder that is then passed to json.loads() as the object_pairs_hook. It ensures that each key in the parsed JSON object is converted to an integer.

Bonus One-Liner Method 5: Using map() and dict() with Unpacking

Combining map(), dict(), and tuple unpacking provides a clever and efficient one-liner to convert dictionary keys to integers.

Here’s an example:

original_dict = {"1": "apple", "2": "banana"}
converted_dict = dict(map(lambda kv: (int(kv[0]), kv[1]), original_dict.items()))

Output:

{1: "apple", 2: "banana"}

This one-liner uses map() to apply a lambda function that converts keys to integers to each key-value pair and then constructs a new dictionary from the resulting iterable.

Summary/Discussion

• Method 1: Dictionary Comprehension. It is the most Pythonic and readable. Best for simple conversions. Not suitable for complex operations.
• Method 2: Using map() Function. Functional programming approach. Good for inline transformations. Might be less readable for those not familiar with functional programming paradigms.
• Method 3: For Loop. Straightforward and explicit. Easiest to understand for beginners. Can become verbose with large or complex dictionaries.
• Method 4: JSON Parsing. Ideal for JSON data manipulation. Involves custom decoding. Overkill for simple dictionaries not in JSON format.
• Method 5: One-Liner with map() and Unpacking. Compact code. Good for simple, quick conversions. Can be less readable due to compactness.