运行Streamlit应用时报ValueError：signal仅在主解释器主线程生效

报错回溯 #

File "C:\Users\jalal\AppData\Local\Programs\Python\Python311\Lib\site-packages\streamlit\runtime\scriptrunner\script_runner.py", line 552, in _run_script
    exec(code, module.__dict__)
File "C:\Users\jalal\python_work\application.py", line 18, in <module>
    app.run(debug=True)
File "C:\Users\jalal\AppData\Local\Programs\Python\Python311\Lib\site-packages\flask\app.py", line 889, in run
    run_simple(t.cast(str, host), port, self, **options)
File "C:\Users\jalal\AppData\Local\Programs\Python\Python311\Lib\site-packages\werkzeug\serving.py", line 1097, in run_simple
    run_with_reloader(
File "C:\Users\jalal\AppData\Local\Programs\Python\Python311\Lib\site-packages\werkzeug\_reloader.py", line 439, in run_with_reloader
    signal.signal(signal.SIGTERM, lambda *args: sys.exit(0))
File "C:\Users\jalal\AppData\Local\Programs\Python\Python311\Lib\signal.py", line 56, in signal
    handler = _signal.signal(_enum_to_int(signalnum), _enum_to_int(handler))
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

涉及文件代码 #

application.py #

from flask import Flask
from flask.templating import render_template
import streamlit as st
import requests
from streamlit_lottie import st_lottie

st.set_page_config(page_title="Consultant Company", page_icon="hammer_and_wrench", layout="wide")

app = Flask(__name__, static_url_path='/static')


@app.route('/')
def index():
    return render_template('index.html', name='home')


if __name__ == "__main__":
    app.run(debug=True)

navigation.py #

import streamlit as st


def navigation():
    try:
        path = st.experimental_get_query_params()['p'][0]
    except Exception as e:
        st.error('Please use the main app.')
        return None
    return path


if navigation() == "home":
    st.title('Home')
    st.write('This is the home page.')

elif navigation() == "results":
    st.title('Results List')
    for item in range(25):
        st.write(f'Results {item}')

elif navigation() == "analysis":
    st.title('Analysis')
    x, y = st.number_input('Input X'), st.number_input('Input Y')
    st.write('Result: ' + str(x+y))

elif navigation() == "examples":
    st.title('Examples Menu')
    st.write('Select an example.')


elif navigation() == "logs":
    st.title('View all of the logs')
    st.write('Here you may view all of the logs.')


elif navigation() == "verify":
    st.title('Data verification is started...')
    st.write('Please stand by....')


elif navigation() == "config":
    st.title('Configuration of the app.')
    st.write('Here you can configure the application')

index.html #

<!DOCTYPE html>
<html>

<head>
  <link rel="stylesheet" type="text/css" href="/static/styles/styles.css">
</head>

<body>
  <div class="dropdown">
    <button class="dropbtn">Dropdown</button>
    <div class="dropdown-content">
      <a href="#">Link 1</a>
      <a href="#">Link 2</a>
      <a href="#">Link 3</a>
    </div>
  </div>
  <ul>

    <li>
      <a class="navbar-brand" href="/">
        <div class="logo-image">
          <img src="/static/images/logo.png" class="img-fluid">
        </div>
      </a>
    </li>
    <li>
      <a href="#" onclick="setURL('http://localhost:8501/?p=analysis')">Analysis</a>
    </li>
    <li>
      <a href="#" onclick="setURL('http://localhost:8501/?p=results')">Results</a>
    </li>
    <li>
      <a href="#" onclick="setURL('http://localhost:8501/?p=examples')">Examples</a>
    </li>


  </ul>
  <iframe src="http://localhost:8501/?p=home" id="streamlit_content" allowfullscreen frameborder="0"
    wmode="transparent">
    Your browser doesn't support iframes
  </iframe>

</body>
<script>
  function setURL(url) {
    document.getElementById('streamlit_content').src = url;
    console.log('Works!')
  }
</script>

</html>

styles.css #

body {
    font-family: 'Trebuchet MS', sans-serif;
    font-weight: bold;
    margin: 0;
     background-color: whitesmoke;
} 

/* #31333f */
ul {
    list-style-type: none;
    font-size: large;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #333;
    position: relative;
    width: 100%;
    height: 3.5rem;
    z-index: 999999;
}
li {
    height: 100%;
    float: left;
}
li a {
    display: block;
    color: white;
    text-align: center;
    padding: 18px 16px;
    height: 100%;
    text-decoration: none;
}

li a:hover:not(.active) {
    background-color: #111;
}

.active {
    background-color: #333;
}

.logo-image {
    width: 46px;
    height: 46px;
    overflow: hidden;
    margin-top: -25%;
}

iframe{
    width: 100%;
    border: none;
    position: fixed;
    height: 100%;
    z-index: 0;
}
.dropbtn {
  background-color: #333;
  color: white;
  padding: 16px;
font-size: large;
  font-family: 'Trebuchet MS', sans-serif;
  font-weight: bold;
  border: none;
  cursor: pointer;
  height: 3.5rem;

}

.dropdown {
  position: fixed;
  right: 0;
  z-index: 9999999999999;
}

.dropdown-content {
  display: none;
  position: absolute;
  background-color: #f9f9f9;
  min-width: 160px;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
  z-index: 9999999;
}

.dropdown-content a {
  color: black;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
}

.dropdown-content a:hover {background-color: #f1f1f1}

.dropdown:hover .dropdown-content {
  display: block;
}

.dropdown:hover .dropbtn {
  background-color: #333;
}

问题原因 #

你将Flask和Streamlit代码混在同一个进程中：application.py里调用了Streamlit的st.set_page_config，而Streamlit本身会启动独立服务线程；同时Flask开启调试模式（debug=True），调试重载器会尝试在非主线程设置信号处理，触发Python信号机制的限制，导致报错。

解决方案 #

Flask和Streamlit是独立的Web框架，需分开作为两个服务运行：

1. 修改application.py，移除Streamlit相关代码 #

from flask import Flask
from flask.templating import render_template

app = Flask(__name__, static_url_path='/static')

@app.route('/')
def index():
    return render_template('index.html', name='home')

if __name__ == "__main__":
    # 指定Flask端口为5000，避免与Streamlit默认的8501端口冲突
    app.run(debug=True, port=5000)

2. 单独启动Streamlit服务 #

打开新的命令提示符，运行以下命令启动navigation.py：

streamlit run navigation.py --server.port 8501

3. 验证服务运行 #

• Flask服务将在http://localhost:5000启动
• Streamlit服务将在http://localhost:8501启动
• 访问Flask地址，iframe会加载Streamlit内容，导航按钮可正常切换页面

内容的提问来源于stack exchange，提问作者arian