Скачать или смотреть Securely Use eval() in Python for Controlled Calculations

Learn how to safely restrict the `eval()` function in Python to evaluate only arithmetic expressions and specific functions, protecting your applications from arbitrary code execution.
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Safely Evaluating Expressions in Python: Controlling eval()

When it comes to evaluating expressions in Python, the built-in eval() function is a powerful tool. However, it poses significant security risks if it's not handled properly. As a developer, you might have encountered situations where you'd like to leverage eval() to create calculators or similar applications. But how do you ensure that only safe operations are allowed?

In this guide, we’ll take a deep dive into how to effectively control the eval() function to only permit arithmetic expressions and certain predefined functions. Let’s explore the steps together!

The Problem with Using eval()

Using eval() can be dangerous because it allows the execution of arbitrary Python code. This means that if a malicious user provides an input string, they can execute harmful commands on your system. Here are some potential dangers:

Execution of harmful commands: Users could execute system commands, modify data, or compromise security.

Data leaks: Users might access sensitive information by exploiting eval().

Given these risks, it’s essential to restrict eval() so that it can only handle safe commands and expressions.

Solution: Using eval() Safely

To use eval() within a controlled environment, follow these steps:

1. Restrict Built-ins

One of the main methods to limit the power of eval() is to remove access to Python's built-in functions. Here’s how to do that:

[[See Video to Reveal this Text or Code Snippet]]

By passing _builtins_ as an empty dictionary to eval(), we effectively prevent any built-in functions from being accessed.

2. Define Allowed Functions

Next, you can allow the use of only certain functions:

Import your custom functions from a separate file (e.g., mymathmodule.py)

Add them to the globs dictionary so they can be accessed safely.

3. Implementing eval() in Your Code

We can now integrate this configuration into your existing calculator code. Here’s how it looks:

[[See Video to Reveal this Text or Code Snippet]]

4. Handling Variables with Local Dictionaries

Remember that if you want to allow variables in the expression, you'll need to handle them carefully. You can pass a local dictionary to store temporary variables while preventing users from overwriting important data.

Passing an empty dictionary prevents any unintended variable assignments, ensuring that only your defined operations can be executed.

Alternatives to eval()

While eval() can be limited for safety, you may also want to consider some alternatives, such as:

Using libraries like NumPy or SymPy to evaluate expressions without resorting to eval().

Creating a parser using libraries like pyparsing or lark to safely parse and evaluate mathematical expressions.

These alternatives can provide more structured ways of accomplishing what you need without the risks associated with eval().

Conclusion

The eval() function can be a helpful tool for evaluating expressions in Python, but it's crucial to use it with caution. By restricted access to built-in functions and defining your own safe functions, you can leverage eval() without compromising security. Always remember, when in doubt, consider alternatives to keep your applications safe.

By following the practices outlined here, you can create a secure environment for your calculator or any other application that requires evaluation of expressions. Happy coding!