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tech_docs/python/asyncio.md

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+For asynchronous programming in Python, `asyncio` stands out as a vital library. It provides a framework that revolves around writing concurrent code using the async/await syntax introduced in Python 3.5. `asyncio` is used for developing server-side applications, database connection libraries, and speed enhancements in web frameworks. Here's a concise reference guide for common use cases with `asyncio`, aiding in understanding and implementing asynchronous programming:
+
+# `asyncio` Reference Guide
+
+## Installation
+`asyncio` is included in the standard library of Python 3.5 and later, so no additional installation is necessary.
+
+## Basic Usage
+
+### Importing asyncio
+```python
+import asyncio
+```
+
+### Running an Async Function
+```python
+async def main():
+    print('Hello')
+    await asyncio.sleep(1)
+    print('World')
+
+# Python 3.7+
+asyncio.run(main())
+```
+
+### Creating Tasks
+```python
+async def say_after(delay, what):
+    await asyncio.sleep(delay)
+    print(what)
+
+async def main():
+    task1 = asyncio.create_task(say_after(1, 'hello'))
+    task2 = asyncio.create_task(say_after(2, 'world'))
+
+    print('Started tasks')
+    # Wait until both tasks are completed
+    await task1
+    await task2
+
+asyncio.run(main())
+```
+
+### Waiting with `asyncio.gather`
+```python
+async def main():
+    # Schedule three calls concurrently
+    await asyncio.gather(
+        say_after(1, 'hello'),
+        say_after(2, 'world'),
+        say_after(3, '!')
+    )
+
+asyncio.run(main())
+```
+
+## Working with I/O Operations
+
+### Using asyncio for Asynchronous I/O
+`asyncio` provides support for asynchronous I/O operations, such as reading and writing to files, network requests, and database operations, using the `aiohttp` library for HTTP requests, for example.
+
+### Example: Asynchronous HTTP Requests
+```python
+import aiohttp
+
+async def fetch(url):
+    async with aiohttp.ClientSession() as session:
+        async with session.get(url) as response:
+            return await response.text()
+
+async def main():
+    html = await fetch('http://python.org')
+    print(html[:100])
+
+asyncio.run(main())
+```
+
+## Event Loop
+
+### Understanding the Event Loop
+The event loop is the core of `asyncio` applications, handling execution of asynchronous tasks, callbacks, and I/O events. Use `asyncio.run()` to run the top-level entry point “main()” function.
+
+### Managing the Event Loop Manually
+For fine-grained control over the event loop, you can manage it manually, which is more common in complex applications and libraries.
+
+```python
+loop = asyncio.get_event_loop()
+try:
+    loop.run_until_complete(main())
+finally:
+    loop.close()
+```
+
+`asyncio` makes it easier to write and manage asynchronous code, facilitating the development of efficient and scalable applications, especially for I/O-bound and high-level structured network code. It's a powerful tool in the Python standard library, enabling developers to leverage asynchronous programming patterns for improved performance.