Скачать или смотреть How to Get the Output Type from Popen stdout in Python

Explore effective ways to handle subprocess output in Python and ensure correct data types using `Popen` and alternative methods.
---
This video is based on the question https://stackoverflow.com/q/63096397/ asked by the user 'Tanatorn Boonprasert' ( https://stackoverflow.com/u/12319355/ ) and on the answer https://stackoverflow.com/a/63097783/ provided by the user 'tripleee' ( https://stackoverflow.com/u/874188/ ) 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: How to get output type from Popen stdout

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 Get the Output Type from Popen stdout in Python

When creating automated grading systems or any application that involves running subprocesses in Python, accurately capturing and interpreting the output can be challenging. One common issue is that the output you receive from stdout is always of type str, regardless of the expected type. This raises the question: How can you effectively obtain the actual type of output from a Popen call?

Understanding the Problem

In the provided example, a function named check_output is designed to execute a Python script (test_file) and capture its output:

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

No matter what the test_file returns (for example, an integer), the output received from the stdout stream is always a string. This presents an issue for type checking and further processing.

The Many Forms of Output

When you're reading from standard output, there are generally two forms that the output can take:

Binary (bytes): The raw output received.

String (str): The output decoded from binary format, either directly (by using .decode()) or automatically (by setting text=True or universal_newlines=True).

Why the Output is Always a String

In Python's subprocess module:

Any data read from stdout using Popen and stored in a variable like stdout is either captured as bytes or immediately converted to str when specified.

This means that if the intention is to work with the output as its original data type (e.g., an integer), additional steps must be taken to convert the string representation.

Improved Solutions

While the initial approach works, there are a few suggestions for improving the code:

1. Use Higher-Level Functions

Instead of using Popen, consider using subprocess.check_output() or its modern alternative, subprocess.run(), which are designed for simpler use cases:

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

This encapsulation returns the output as bytes, and you can decode it right where you process the results.

2. Directly Import and Call Functions

If your goal is to test the function or script directly rather than checking the standard output:

Avoid the subprocess call and directly import the necessary code:

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

This way, you work with the actual Python data types, avoiding the complexities of handling stdout.

Conclusion

In summary, while Popen is a useful tool for invoking subprocesses, using high-level functions like subprocess.check_output() or directly calling imported functions generally leads to cleaner and more maintainable code. By understanding and correctly handling the output types, you can significantly reduce complexity in your code and ensure that you are working with the data in its intended form.

If you're dealing with subprocess outputs in Python, consider these strategies for a more effective and less error-prone approach to automation and testing.