Jupyter运行prompt_toolkit代码报RuntimeError：事件循环已运行的解决方法

我写了一个带自动补全的水果价格查询脚本，用prompt_toolkit实现，在VS Code里运行正常，但在Jupyter环境执行时总是报错：RuntimeError: This event loop is already running，需要解决这个问题。

原代码 #

from prompt_toolkit import prompt
from prompt_toolkit.completion import WordCompleter

# 水果价格字典
fruits = {
    "apple": 2.5,
    "orange": 3.0,
    "pinapple": 5.0,
    "banana": 1.5,
    "kiwi": 4.0,
    "mango": 6.0
}

# 创建水果补全器
fruits_completer = WordCompleter(list(fruits.keys()))

# 提示用户输入水果名称
fruit_input = prompt("Type the name of the fruit: ", completer=fruits_completer)

# 显示所选水果的价格
price = fruits.get(fruit_input)

if price:
    print(f"The price of the {fruit_input} is: {price}")
else:
    print("The fruit is not in the list")

注：原代码存在变量名错误，已修正fruits变量覆盖问题

错误原因 #

Jupyter Notebook/Lab本身已经启动了一个异步事件循环，而prompt_toolkit的prompt()函数默认会尝试创建新的事件循环，导致循环冲突，触发上述错误。

解决方法 #

方案一：使用异步版本prompt配合Jupyter事件循环 #

利用prompt_toolkit的prompt_async()异步函数，通过Jupyter现有事件循环运行：

import asyncio
from prompt_toolkit import prompt_async
from prompt_toolkit.completion import WordCompleter

fruits = {
    "apple": 2.5,
    "orange": 3.0,
    "pinapple": 5.0,
    "banana": 1.5,
    "kiwi": 4.0,
    "mango": 6.0
}

fruits_completer = WordCompleter(list(fruits.keys()))

async def get_fruit_price():
    fruit_input = await prompt_async("Type the name of the fruit: ", completer=fruits_completer)
    price = fruits.get(fruit_input)
    if price:
        print(f"The price of the {fruit_input} is: {price}")
    else:
        print("The fruit is not in the list")

# 在Jupyter现有事件循环中运行
asyncio.create_task(get_fruit_price())

方案二：使用nest_asyncio允许嵌套事件循环 #

安装nest_asyncio库后，让Jupyter支持嵌套事件循环，原代码可直接运行：

1. 安装依赖库：

pip install nest_asyncio

2. 修改后的代码：

import nest_asyncio
from prompt_toolkit import prompt
from prompt_toolkit.completion import WordCompleter

# 允许嵌套事件循环
nest_asyncio.apply()

fruits = {
    "apple": 2.5,
    "orange": 3.0,
    "pinapple": 5.0,
    "banana": 1.5,
    "kiwi": 4.0,
    "mango": 6.0
}

fruits_completer = WordCompleter(list(fruits.keys()))

fruit_input = prompt("Type the name of the fruit: ", completer=fruits_completer)

price = fruits.get(fruit_input)
if price:
    print(f"The price of the {fruit_input} is: {price}")
else:
    print("The fruit is not in the list")

预期运行效果 #

运行后提示输入水果名称，输入前缀如app时会弹出apple补全选项，选择回车后显示对应价格：

Type the name of the fruit: app
Type the name of the fruit: apple
The price of the apple is: 2.5

内容的提问来源于stack exchange，提问作者Javier