title: Telethon leads to `RuntimeWarning: coroutine 'MessageMethods.send_message' was never awaited`
body: <p>I'm trying to run <a href="https://docs.telethon.dev/en/latest/" rel="noreferrer">this first code snippet</a> provided by the Telethon documentation. But, after multiple problems (<a href="https://stackoverflow.com/a/60978983/4999991">here</a> and <a href="https://stackoverflow.com/q/55196673/4999991">here</a>), I ended up with this modified version:</p>
  
  <pre class="lang-py prettyprint-override"><code>import os
  import sys
  from telethon.sync import TelegramClient, events
  
  # import nest_asyncio
  # nest_asyncio.apply()
  
  session_name = "&lt;session_name&gt;"
  api_id = &lt;api_id&gt;
  api_hash = "&lt;api_hash&gt;"
  
  
  os.chdir(sys.path[0])
  
  if f"{session_name}.session" in os.listdir():
      os.remove(f"{session_name}.session")
  
  async with TelegramClient(session_name, api_id, api_hash) as client:
     client.send_message('me', 'Hello, myself!')
     print(client.download_profile_photo('me'))
  
     @client.on(events.NewMessage(pattern='(?i).*Hello'))
     async def handler(event):
        await event.reply('Hey!')
  
     client.run_until_disconnected()
  </code></pre>
  
  <p>However now I'm getting these warnings:</p>
  
  <pre>
  usr/local/lib/python3.7/site-packages/ipykernel_launcher.py:23: RuntimeWarning: coroutine 'MessageMethods.send_message' was never awaited
  RuntimeWarning: Enable tracemalloc to get the object allocation traceback
  /usr/local/lib/python3.7/site-packages/ipykernel_launcher.py:24: RuntimeWarning: coroutine 'DownloadMethods.download_profile_photo' was never awaited
  RuntimeWarning: Enable tracemalloc to get the object allocation traceback
  /usr/local/lib/python3.7/site-packages/ipykernel_launcher.py:30: RuntimeWarning: coroutine 'UpdateMethods._run_until_disconnected' was never awaited
  RuntimeWarning: Enable tracemalloc to get the object allocation traceback
  </pre>
  
  <p>when running the code on Jupyter. Now here are my questions:</p>
  
  <ul>
  <li>what those warning messages mean and how should I address them?</li>
  <li>what is the expected result of this code if working properly? Should I receive a message in Telegram or something? Because I don't recive any messages other than the signin code. </li>
  <li>What does the <code>@</code> symbol at the beginning of the <code>@client.on...</code> line mean? what does that line is supposed to do? From this line onwards I do not understand the code. Would appreciate if you could help me understand it.</li>
  </ul>