Python [Invalid syntax] with async def

Question

I am trying write discord bots using Python, I have come across and threw together this bot.

import discord
import asyncio
import random

client = discord.Client()
inEmail = input("Email:")
inPassword = input("Passwd:")

async def background_loop():
    await client.wait_until_ready()
    while not client.is_closed:
        channel = client.get_channel("************")
        messages = ["Hello!", "How are you doing?", "Testing!!"]
        await client.send_message(channel, random.choice(messages))
        await asyncio.sleep(120)

client.loop.create_task(background_loop())
client.run(inEmail, inPassword)

Yet when I tried to run it, I received a SyntaxError:

File "1.py", line 7
  async def background_loop():
     ^
SyntaxError: invalid syntax

Why is that? I have never received that before when I tested it.

Answer 1

Asynchronous requests were introduced to Python in v3.3, if you're running Python prior to v3.3 (including v2.X), you'll have to install a newer version of Python.

---

Only if you are running Python 3.3: asyncio is not part of the stdlib, you'll need to install it manually from pypi:

pip install asyncio

The async and await keywords are only valid for Python 3.5 or newer. If you're using Python 3.3 or 3.4, you will need to make the following changes to your code:

1. Use the @asyncio.coroutine decorator instead of the async statement:

async def func():
    pass

# replace to:

@asyncio.coroutine
def func():
    pass

2. Use yield from instead of await:

await coroutine() 

# replace to:

yield from coroutine()

Here is an example of what your function need to change into (if you're on 3.3-3.4):

import asyncio

@asyncio.coroutine 
def background_loop():
    yield from client.wait_until_ready()
    while not client.is_closed:
        channel = client.get_channel("************")
        messages = ["Hello!", "How are you doing?", "Testing!!"]
        yield from client.send_message(channel, random.choice(messages))
        yield from asyncio.sleep(120)

The aforementioned syntax is still supported in newer versions of Python 3, but it is recommended to use await and async if there's no need to support for Python 3.3-3.4. You can refer back to this documentation, here's a short snippet:

The async def type of coroutine was added in Python 3.5, and is recommended if there is no need to support older Python versions.

---

Aside:

discord.py currently supports 3.4.2-3.6.6, (It does not support 3.3-3.4.1, 3.7 as of January 2019).

For developing with discord.py, I suggest using the discord.py rewrite branch:

discord.py-rewrite supports 3.5.3-3.7.