Phase 3: How the Internet & APIs Actually Work · ~35 minutes · Python · asyncio

async/await in Practice

Forget await and Python doesn't crash. It hands you a coroutine object instead of your actual result — a real value, just entirely the wrong one.

Hiring signal: Recognizes a coroutine object where a real value was expected as a missing-await bug, instantly

What you will learn

Use async def and await correctly to convert a synchronous script
Explain the event loop as a single-threaded scheduler juggling waiting tasks, not parallelism
Diagnose a real, reproduced missing-await bug
Predict what a snippet missing an await actually returns

Introduction

Type: Learn Languages: Python, asyncio Prerequisites: Lesson 03 (Why Blocking I/O Is a Problem) Time: ~35 minutes

Objective

Learning objectives

Use async def and await correctly to convert a synchronous script
Explain the event loop as a single-threaded scheduler juggling waiting tasks, not parallelism
Diagnose a real, reproduced missing-await bug
Predict what a snippet missing an await actually returns

What you're building

Take a synchronous script you wrote for Lesson 03's lab (or write a fresh one with 3+ independent simulated API calls):

Convert every relevant function to async def/await, and combine the independent calls with asyncio.gather()
Verify the converted version produces identical results to the original synchronous version
Measure and print both versions' real elapsed time, confirming the speedup still holds after the conversion
Deliberately reproduce this lesson's missing-await bug in a separate, clearly-commented example: show the RuntimeWarning, the wrong type(), and then the corrected version with await restored

async def get_price(item):
    await asyncio.sleep(0.1)
    return 19.99

async def main():
    price = get_price("widget")
    print(f"Price: ${price}")

What does this actually print?

price is a coroutine object — get_price was never awaited, so it never actually ran and never produced 19.99. f-strings, like print(), work on any object by calling its default string representation, so f"Price: ${price}" doesn't crash — it silently produces something like "Price: <coroutine object get_price at 0x...>", visibly wrong to a human reading the output but not an error Python itself catches. This is precisely this lesson's most dangerous case: no crash, no warning a busy log would surface clearly, just an obviously-broken-looking but non-fatal result.

Unlock the full lesson

You've read the first 2 sections. The rest of this lesson covers The Problem, Check Yourself, Key Terms & Next — plus a hands-on lab, quiz, and project artifact.

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