The code will be:
import sys
@client.event()
async def on_ready()
user = int(sys.argv[1])
user = await client.fetch_user(user)
message = str(sys.argv[2])
await user.send(message)
Now you can go python3 bot.py <userid> “<message>“ The message must be in “” the user id must be the user id and not the name. If you dont want to specify the user/message everytime,Just change the variable