Why Does the Spawn Child Process Print to stdout Only After Execution with Python?

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Understanding Output Buffering in Python's Child Process

The Problem Explained

Here's a simplified version of what the issue looks like:

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

Why Does Output Buffering Happen?

Python buffers output by default, particularly when it's not running in an interactive mode. This means that it collects output data before writing it to stdout, which is why you see the delayed printing. Let's look into how we can address this issue.

Solutions to Enable Real-time Output

1. Use the -u Flag

You can run Python in unbuffered mode by using the -u flag when calling the Python interpreter. This tells Python to interactively flush the output, which can be done like so:

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

2. Set the PYTHONUNBUFFERED Environment Variable

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

3. For Cleaner Code, Skip Temporary Files

Instead of creating temporary files to pass multitudes of Bash commands or Python scripts, you can directly write and feed your Python code to the stdin of the child process. Here’s how you can implement that:

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

Expected Output

Using the above approach, your output will appear in real-time, something like this:

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

Conclusion