Скачать или смотреть How to Use exec in Python Without Accessing Outside Variables

Discover how to safely use the `exec` command in Python while ensuring that it does not access any outside variables by providing an empty globals dictionary.
---
This video is based on the question https://stackoverflow.com/q/69298051/ asked by the user 'DivyeshLakhotia' ( https://stackoverflow.com/u/16260287/ ) and on the answer https://stackoverflow.com/a/69298069/ provided by the user 'U13-Forward' ( https://stackoverflow.com/u/8708364/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Ignore outside variables in exec

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Use exec in Python Without Accessing Outside Variables

The exec command in Python is a powerful function that allows you to execute dynamic Python code. However, one common issue developers encounter is how to control the environment in which this code runs, especially when it comes to variable accessibility. In this guide, we will explore how to use the exec command without allowing access to any outside variables.

The Problem with exec

When you use the exec command, it executes the provided code in the current scope. This can be problematic if your code relies on variables that might inadvertently be accessed from the surrounding context. For example, consider the following code:

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

In this snippet, exec prints the value of x, which is 2. However, what if you want to execute code within exec that should not have access to x? You might want the code to fail, resulting in a NameError for the undefined variable:

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

What you expect here is that the code should raise an error saying that x is not defined.

The Solution: Using an Empty Globals Dictionary

To ensure that exec does not have access to any outside variables, you can pass an empty dictionary as the globals parameter. This effectively isolates the execution environment of the code. Here’s how to implement this:

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

Explanation of the Code

Defining a Variable: We first define a variable x with a value of 2.

Running exec with a Variable: The first call to exec("print(x)") prints 2 because x is accessible in the current scope.

Isolation Using Globals: In the second call, exec("print(x)", {}), we provide an empty dictionary {} as the globals parameter. This means the executed code has no access to any variables defined outside of it, resulting in a NameError as expected.

Understanding the exec Function

According to the official Python documentation, the exec function can be defined as follows:

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

source: This is the code you want to execute, which can be a string or a code object.

globals: The variables that should be accessible in the global context. It must be a dictionary.

locals: The variables that should be accessible locally. By default, it will use the current local scope.

If only globals is specified, locals will default to it.

Conclusion

Using exec in Python can be quite powerful, but it also requires caution, especially regarding variable scopes. By providing an empty dictionary to the globals parameter, you can ensure that your executed code does not have access to any variables defined outside of it, effectively protecting your execution environment.

This approach helps in maintaining the integrity of your code and avoids potential conflicts with unexpected variables. If you're using exec, consider implementing this practice to improve reliability and security.

If you have any questions or further topics of interest regarding Python's exec, feel free to leave a comment below!