Correct Code Fails in Python due to Execution Context

When “Correct” Code Fails: The Hidden Context of Tutorials Have you ever run into that classic frustration where you copy a code snippet—verbatim—from a tutorial, and it completely breaks on your machine? That was me today. 😅 I was implementing a PDF loader for a RAG pipeline using LangChain, and I copied this snippet straight from the tutorial material: # The tutorial code: async for page in loader.alazy_load():   pages.append(page) The Error: SyntaxError: 'async for' outside async function The Investigation: Why did it work perfectly for the instructor but fail for me? Context, as usual, was the culprit. The tutorial was written for a Jupyter Notebook (.ipynb) environment, which supports top-level await—meaning asynchronous code can run directly inside a cell. I was working in a standard Python script (.py), where async rules are far stricter. You can’t use await or async for in the global scope. Everything has to live inside an event loop. The Fix: I wrapped the logic in an async function and executed it properly using asyncio. This is the working pattern: import asyncio async def load_docs():   pages = []   async for page in loader.alazy_load():     pages.append(page)   return pages if __name__ == "__main__":   # The crucial bridge between sync and async   pages = asyncio.run(load_docs()) The Takeaway: This drove a simple point home: a code snippet can be syntactically “correct” and still fail when the execution context changes. When debugging, don’t just look at what the code is doing—look at where it’s running. Abdullahi Badrudeen Chris Ekwugum #Python #AsyncIO #SoftwareEngineering #LangChain #RAG #LLMEngineering #BackendDevelopment #Debugging #DeveloperLessons #CodingInPublic #LearningInPublic

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