Eval() vs. ast.literal_eval(): Which Python Function Is Safer for User Input?

Weighing eval() and ast.literal_eval() in Python Security

When handling user input, it's imperative to prioritize security. eval(), a powerful Python function, often arises as a potential solution, but concerns surround its potential risks. This article delves into the differences between eval() and ast.literal_eval(), highlighting their security implications.

Understanding eval()

eval() evaluates the input as soon as its entered, regardless of subsequent type checking. This means that malicious input can be executed before you have a chance to mitigate it. The following code snippet demonstrates this vulnerability:

datamap = eval(input('Provide some data here: '))

Introducing ast.literal_eval()

ast.literal_eval() is a safer alternative to eval() that doesn't execute code until it's determined to be safe. It validates the input to ensure it represents a Python literal, such as a dictionary, list, or tuple. If the input doesn't fit this format, it raises an exception, preventing malicious code from running.

try:
    datamap = ast.literal_eval(input('Provide some data here: '))
except ValueError:
    return # Handle invalid input

Best Practices

For security reasons, it's highly recommended to use ast.literal_eval() whenever possible, especially when dealing with untrusted or uncertain input. Eval() should be avoided due to its potential for exploitation.

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