Solving FileNotFoundError in Python Subprocess Calls: A Step-By-Step Guide

Learn how to fix incorrect path issues in Python scripts when using subprocess calls. This guide provides solutions with clear examples, ensuring smooth execution of scripts across directories. --- This video is based on the question https://stackoverflow.com/q/71587399/ asked by the user 'Marie' ( https://stackoverflow.com/u/17107138/ ) and on the answer https://stackoverflow.com/a/71587803/ provided by the user 'Cow' ( https://stackoverflow.com/u/11355926/ ) 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: Incorrect path in Python Script when called from remote subprocess 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. --- Solving FileNotFoundError in Python Subprocess Calls: A Step-By-Step Guide If you've ever faced issues with file paths when executing Python scripts from different directories, you're not alone. A common problem arises when trying to call a script, let’s say worker.py, from another script, such as main.py. Often, you may encounter a FileNotFoundError because the script is not executing in the expected directory. In this guide, we'll explore this issue and how to resolve it effectively. The Problem In the scenario provided, we have two Python scripts located in different folders: main.py located in the main folder worker.py located in the worker folder, which accesses a file named parameters.txt located in a data subfolder within the worker folder. When worker.py is executed directly, it can find parameters.txt without any issues. However, if it's called from main.py using a subprocess, like so: [[See Video to Reveal this Text or Code Snippet]] it results in a FileNotFoundError, indicating that the script is looking for parameters.txt in an unexpected directory. This issue arises because the working directory doesn't match the expectation of where the script is located. Understanding the Issue When you run a Python script, it starts in the current working directory from which you invoked it. In this case, when you call worker.py from main.py, the working directory is still set to where main.py resides, not where worker.py is located. That is why the path for parameters.txt is being interpreted incorrectly. The Solution To solve this problem, you can specify the cwd (current working directory) argument when using subprocess.call(). By doing this, you instruct the subprocess where to execute the script. Here’s how you can implement this solution: Step-by-Step Implementation Import Necessary Modules: You'll need to import subprocess and some functions from os to handle paths correctly. [[See Video to Reveal this Text or Code Snippet]] Set the Current Directory: Capture the current working directory and change the working directory to where worker.py is located. [[See Video to Reveal this Text or Code Snippet]] Execute the Subprocess Command: Use subprocess.call() with the specified working directory to run the worker script. [[See Video to Reveal this Text or Code Snippet]] Example Worker Code For testing purposes, here is an example of what worker.py might look like to read the file: [[See Video to Reveal this Text or Code Snippet]] Assuming test.txt contains "hello!", running this will output: [[See Video to Reveal this Text or Code Snippet]] Conclusion By effectively setting the current working directory in your subprocess call with the cwd argument, you can resolve FileNotFoundError issues when executing scripts from different directories. This allows for smoother script execution and enables your worker.py to access parameters.txt without any path-related issues. With this guide, you should now be able to handle subprocess calls in Python effectively, ensuring that each script works independently while still being able to communicate as needed. Happy coding!