Python – Convert String to List of dictionaries

Given List of dictionaries in String format, Convert into actual List of Dictionaries.

Input : test_str = [“[{‘Gfg’ : 3, ‘Best’ : 8}, {‘Gfg’ : 4, ‘Best’ : 8}]”] 
Output : [[{‘Gfg’: 3, ‘Best’: 8}, {‘Gfg’: 4, ‘Best’: 8}]] 
Explanation : String converted to list of dictionaries. 

Input : test_str = [“[{‘Gfg’ : 3, ‘Best’ : 8}]”] 
Output : [[{‘Gfg’: 3, ‘Best’: 8}]] 
Explanation : String converted to list of dictionaries.

Method #1:  Using json.loads() + replace()

The combination of above functions can be used to solve this problem. In this, we replace the internal Strings using replace() and dictionary list is made using loads().

Python3

# Python3 code to demonstrate working of
# Convert String to List of dictionaries
# Using json.loads + replace()
import json

# initializing string
test_str = ["[{'Gfg' : 3, 'Best' : 8}, {'Gfg' : 4, 'Best' : 9}]"]

# printing original string
print("The original string is : " + str(test_str))

# replace() used to replace strings
# loads() used to convert
res = [json.loads(idx.replace("'", '"')) for idx in test_str]

# printing result
print("Converted list of dictionaries : " + str(res))

Output

The original string is : ["[{'Gfg' : 3, 'Best' : 8}, {'Gfg' : 4, 'Best' : 9}]"]
Converted list of dictionaries : [[{'Gfg': 3, 'Best': 8}, {'Gfg': 4, 'Best': 9}]]

Method #2: Using eval()

This is one of the ways in which this task can be performed. The eval(), internally evaluates the data type and returns required result.

Python3

# Python3 code to demonstrate working of
# Convert String to List of dictionaries
# Using json.loads + replace()

# initializing string
test_str = "[{'Gfg' : 3, 'Best' : 8}, {'Gfg' : 9, 'Best' : 9}]"

# printing original string
print("The original string is : " + str(test_str))

# eval() used to convert
res = list(eval(test_str))

# printing result
print("Converted list of dictionaries : " + str(res))

Output

The original string is : [{'Gfg' : 3, 'Best' : 8}, {'Gfg' : 9, 'Best' : 9}]
Converted list of dictionaries : [{'Gfg': 3, 'Best': 8}, {'Gfg': 9, 'Best': 9}]

Time Complexity: O(n)
Auxiliary Space: O(n)

Method #4: Using regular expression and literal_eval()

Use regular expressions and the ast.literal_eval() function. This method involves using a regular expression to match all the dictionary literals in the input string and then passing each matched string to ast.literal_eval() to convert it to a dictionary object. 

Step-by-step approach:

• Import the necessary modules, re and ast.
• Initialize a test string with a list of dictionaries.
• Define a regular expression pattern to match dictionary literals.
• Find all matches of dictionary literals in the input string using re.findall() method.
• Use ast.literal_eval() to convert each matched string to a dictionary object.
• Replace all single quotes with double quotes in each matched string before evaluating them using ast.literal_eval().
• Store the resulting dictionary objects in a list using list comprehension.
• Print the list of dictionaries.

Below is the implementation of the above approach:

Python3

import re
import ast

# initializing string
test_str = ["[{'Gfg' : 3, 'Best' : 8}, {'Gfg' : 4, 'Best' : 9}]"]

# define regular expression pattern to match dictionary literals
pattern = r"{[^{}]+}"

# find all matches of dictionary literals in input string
matches = re.findall(pattern, test_str[0])

# use ast.literal_eval() to convert each matched string to a dictionary object
res = [ast.literal_eval(match.replace("'", '"')) for match in matches]

# printing result
print("Converted list of dictionaries: ", res)

Output

Converted list of dictionaries:  [{'Gfg': 3, 'Best': 8}, {'Gfg': 4, 'Best': 9}]

Time complexity: The regular expression matching operation takes O(n) time where n is the length of the input string.
Auxiliary space: O(m) auxiliary space to store each matched string temporarily in memory during the evaluation process.