How to convert a String representation of a Dictionary to a dictionary in Python ?

To convert a string representation of a dictionary into a Python dictionary, you can use the following methods, depending on the string’s format and safety requirements:

1. Using ast.literal_eval() (Recommended for Python-Style Strings)

Use Case: Safely evaluate strings containing Python literals (e.g., None, True, single quotes).

Example:

import ast

# String with Python-style syntax (single quotes, None, booleans)
s = "{'name': 'Alice', 'age': 30, 'is_student': False, 'pet': None}"

# Convert to a dictionary
d = ast.literal_eval(s)

print(d)
# Output: {'name': 'Alice', 'age': 30, 'is_student': False, 'pet': None}

Features:

• Handles Python-specific syntax (e.g., None, True/False).
• Safe: Only parses literals, not arbitrary code.

2. Using json.loads() (For JSON-Compliant Strings)

Use Case: Strings formatted as JSON (double quotes, true/false/null).

Example:

import json

# JSON-style string (double quotes, lowercase booleans, null)
s = '{"name": "Alice", "age": 30, "is_student": false, "pet": null}'

# Convert to a dictionary
d = json.loads(s)

print(d)
# Output: {'name': 'Alice', 'age': 30, 'is_student': False, 'pet': None}

Notes:

• JSON requires double quotes (") and lowercase true/false/null.
• Converts JSON null to Python None.

3. Using eval() (Unsafe, Not Recommended)

Use Case: Only use if you fully trust the input string (security risk).

Example:

s = "{'name': 'Alice', 'age': 30, 'is_student': False}"

# Convert to a dictionary (UNSAFE!)
d = eval(s)

print(d)
# Output: {'name': 'Alice', 'age': 30, 'is_student': False}

Warnings:

• Security Risk: Executes arbitrary code (e.g., s = "__import__('os').system('rm -rf /')" would delete files!).
• Avoid unless the input is fully controlled.

Key Differences

Method	Syntax Support	Safety	Use Case
ast.literal_eval()	Python literals (None, True, etc.)	Safe	General-purpose (recommended)
json.loads()	JSON format (null, true, false)	Safe	JSON data from APIs/files
eval()	Any Python code (including functions)	Unsafe	Avoid unless input is fully trusted

Handling Edge Cases

1. Single vs. Double Quotes

Convert single quotes to double quotes for JSON compatibility:

s = "{'name': 'Alice'}"
s_fixed = s.replace("'", '"')  # Convert to {"name": "Alice"}
d = json.loads(s_fixed)

2. JSON true/false/null to Python True/False/None

json.loads() automatically converts:

• true → True
• false → False
• null → None

3. Malformed Strings

Handle errors gracefully:

s = "{'name': 'Alice', age: 30}"  # Missing quotes around 'age'

try:
    d = ast.literal_eval(s)
except SyntaxError:
    print("Invalid string format!")

Full Workflow Example

import ast

def string_to_dict(s):
    try:
        return ast.literal_eval(s)
    except (SyntaxError, ValueError):
        print("Error: Invalid dictionary format")
        return {}

# Test with valid and invalid strings
valid_s = "{'name': 'Alice', 'age': 30}"
invalid_s = "{'name': 'Alice', age: 30}"  # Missing quotes

print(string_to_dict(valid_s))    # {'name': 'Alice', 'age': 30}
print(string_to_dict(invalid_s))  # Error: Invalid dictionary format → {}

Summary

• Use ast.literal_eval() for Python-style strings (safest and most flexible).
• Use json.loads() for JSON-formatted strings.
• Avoid eval() due to security risks.