Python Security: `eval()` vs. `ast.literal_eval()` – Which Should You Use?

Using Python's eval() vs. ast.literal_eval()

Evaluating user-provided data is a common task in Python. However, it's important to do so safely to avoid potential security vulnerabilities. This article compares eval() and ast.literal_eval() for this purpose, addressing concerns about the former's perceived dangers.

eval(): A Risky Approach

Eval() directly executes the provided data as Python code. While seemingly convenient, this can be highly dangerous if the input is malicious. It could lead to arbitrary code execution, exposing your application to security breaches.

ast.literal_eval(): A Safer Alternative

Ast.literal_eval() is a dedicated function for evaluating literal Python data types, such as dictionaries and lists. Unlike eval(), it strictly validates the input and raises an exception if it's not a valid datatype. This prevents the execution of arbitrary code, making it a safer choice.

The key distinction between eval() and ast.literal_eval() lies in the timing of evaluation. Eval() immediately executes the input, while ast.literal_eval() performs validation first. Therefore, attempting to check the type of datamap after using eval() will be ineffective as the data has already been evaluated.

Recommendation

It's strongly recommended to use ast.literal_eval() over eval() for evaluating user-provided data. Its stringent validation prevents potential security vulnerabilities and provides a more robust approach for handling input.

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