Python - Converting list string to dictionary

Converting a list string to a dictionary in Python involves mapping elements from the list to key-value pairs. A common approach is pairing consecutive elements, where one element becomes the key and the next becomes the value. This results in a dictionary where each pair is represented as a key-value entry.

Using dictionary comprehension

Dictionary comprehension can be used for the construction of a dictionary and the split function can be used to perform the necessary splits in a list to get the valid key and value pair for a dictionary. 

a = '[Nikhil:1, Akshat:2, Akash:3]'
res = {
  
    # Extract key and value, converting value to integer
    item.split(":")[0]: int(item.split(":")[1]) 
  
    for item in a[1:-1].split(", ")
}
print(res)

{'Nikhil': 1, 'Akshat': 2, 'Akash': 3}

Explanation:

• String Slicing: a[1:-1] removes the first ([) and last (]) characters from the string, leaving only the substring: "Nikhil:1, Akshat:2, Akash:3".
• Splitting by Comma: .split(", ") creates a list like ["Nikhil:1", "Akshat:2", "Akash:3"].
• Dictionary Comprehension: For each item in that list, item.split(":")[0] becomes the dictionary key, and int(item.split(":")[1]) becomes the value.

Let's explore more methods to convert list string to dictionary.

Using ast.literal_eval

If list string is in a Python-like format ('[("Nikhil", 1), ("Akshat", 2), ("Akash", 3)]'), we can use the built-in ast.literal_eval function to safely parse it into a Python object. Then, if the parsed object is a list of key-value pairs (tuples), we can convert it to a dictionary with dict().

import ast
a = '[("Nikhil", 1), ("Akshat", 2), ("Akash", 3)]'
# evaluate the string to a list of tuples
b = ast.literal_eval(a)
res = dict(b)
print(res)

{'Nikhil': 1, 'Akshat': 2, 'Akash': 3}

Explanation:

• ast.literal_eval(a) converts the string into an actual Python list of tuples-[('Nikhil', 1), ('Akshat', 2), ('Akash', 3)].
• dict(b) takes that list of (key, value) tuples and constructs a dictionary-[('Nikhil', 1), ('Akshat', 2), ('Akash', 3)].

Using re.findall()

re.findall() extract key-value pairs from a string and convert them into a dictionary. It efficiently matches patterns for keys and values, then uses dict() to create the dictionary.

import re
a = '[Nikhil:1, Akshat:2, Akash:3]'
# Use regular expression to extract key-value pairs
res = dict(re.findall(r'(\w+):(\d+)',a))
print(res)

{'Nikhil': '1', 'Akshat': '2', 'Akash': '3'}

Explanation:

• re.findall(r'(\w+):(\d+)', a) extracts key-value pairs from the string a, where \w+ matches the key (letters, numbers, underscores) and \d+ matches the value (digits), returning a list of tuples.
• dict(...) converts the list of tuples into a dictionary, using the first element of each tuple as the key and the second as the value.

Using for Loop

For loop iterates through the string, splits each item into key-value pairs and constructs the dictionary by converting values to integers.

a = '[Nikhil:1, Akshat:2, Akash:3]'
# Initialize an empty dictionary
res = {}
# Iterate through the string and convert to dictionary
for item in a[1:-1].split(", "):
    key, value = item.split(":")
    res[key] = int(value)
print(res)

{'Nikhil': 1, 'Akshat': 2, 'Akash': 3}

Explanation:

• a[1:-1].split(", ") removes the brackets [ ] and splits the string on ", " to get items like "Nikhil:1".
• Loop and Split Each Item: For each item, key, value = item.split(":") separates the name from the number.
• Build the Dictionary: res[key] = int(value) converts the number to an integer and stores the key-value pair in res.