Create a Dictionary from a String

The task of creating a dictionary from a string in Python often involves converting a string representation of a dictionary into an actual Python dictionary.

For example, a string like "{'A':13, 'B':14, 'C':15}" represents a dictionary with keys 'A', 'B', and 'C' mapped to their respective values. The goal here is to transform this string into a Python dictionary. After the transformation, the dictionary will look like this: {'A': 13, 'B': 14, 'C': 15}.

Using ast.literal_eval()

ast.literal_eval() is a efficient method to evaluate strings containing Python literals. It can convert strings that represent basic Python data structures such as dictionaries, lists and tuple into their corresponding Python objects. Unlike eval(), ast.literal_eval() is much safer as it only evaluates literals and does not allow execution of arbitrary code.

import ast
s = "{'A':13, 'B':14, 'C':15}"

res = ast.literal_eval(s)
print(res, type(res))

{'A': 13, 'B': 14, 'C': 15} <class 'dict'>

Explanation: ast.literal_eval(s) to safely convert the string s into a dictionary. It evaluates the string as a Python literal, ensuring security by only allowing basic data structures. The result is stored in res .

Using json.loads()

json.loads() from the json module that parses a string in JSON format and converts it into a Python dictionary. While json.loads() is primarily designed for working with JSON data, it can also be used for parsing dictionaries if the string uses double quotes as JSON format requires .

import json
s = "{'A':13, 'B':14, 'C':15}".replace("'", '"')
res = json.loads(s)

print(res,type(res))

{'A': 13, 'B': 14, 'C': 15} <class 'dict'>

Explanation: This code replaces single quotes with double quotes to make the string JSON-valid, then uses json.loads() to parse it into a Python dictionary. The result is printed along with its type.

Using eval()

eval() is a built-in Python function that parses and evaluates a string as a Python expression. It can handle complex expressions and can be used to evaluate a string representation of a dictionary. However, eval() poses significant security risks when used with untrusted input, as it allows the execution of arbitrary code.

s = "{'A':13, 'B':14, 'C':15}"
res = eval(s)

print(res)

{'A': 13, 'B': 14, 'C': 15}

Explanation: eval(s) evaluate the string s as a Python expression. Since the string s represents a dictionary, eval() converts it into an actual Python dictionary. The result is stored in res .

Using exec()

exec() is another Python built-in function, similar to eval(), but is more general-purpose. It can execute arbitrary Python code and is used when the code in the string may contain multiple Python statements. Like eval(), exec() comes with the same security risks when working with untrusted input.

s = "{'A':13, 'B':14, 'C':15}"
exec(f"res = {s}")

print(res)

{'A': 13, 'B': 14, 'C': 15}

Explanation: This code uses f"res = {s}" to embed the string s into an assignment expression and exec() then executes this string as Python code, assigning the dictionary to res.