带烧瓶的RPI dht22:无法将第4行设置为输入-等待PulseIn消息超时 [英] RPI dht22 with flask: Unable to set line 4 to input - Timed out waiting for PulseIn message

问题描述

我正在尝试制作一个可通过DHT22提供温度和湿度的Raspberry Pi 3 REST API.整个代码:

I'm trying to make a Raspberry Pi 3 REST API that provides temperature and humidity with DHT22. The whole code:

from flask import Flask, jsonify, request
from sds011 import SDS011
from adafruit_dht import DHT22
import board
import os
import time

app = Flask(__name__)
dht = DHT22(board.D4)

def get_dht_data():
    while True:
        try:
            temperature, humidity = dht.temperature, dht.humidity
            print(temperature, humidity)
            if temperature is not None and humidity is not None:
                return temperature, humidity
            else:
                raise
        except:
            time.sleep(0.5)

@app.route('/', methods=['GET'])
def status():
    temperature, humidity = get_dht_data()

    return jsonify({
        'temperature': temperature,
        'humidity': humidity
    })

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

我使用了 https://github.com/adafruit/Adafruit_CircuitPython_DHT

但是，当我启动服务器时，它显示消息

However, when I start server, it shows message

无法将第4行设置为输入"

'Unable to set line 4 to input'

，温度和湿度始终为None.如果我不运行flask应用程序，而仅运行DHT代码，则它可以工作.

and temperature and humidity is always None. If I don't run flask app but just DHT code, it works.

推荐答案

简短答案

删除debug=True并享受. :-)

Short answer

Remove debug=True and enjoy. :-)

这个问题使我发疯，但我想我找到了根本原因！就我而言，我将DHT22对象封装在另一个对象中，如下所示:

This problem drove me nuts but I think I found the root cause! In my case, I was encapsulating the DHT22 object in another object, like so:

...
class DHT22Custom:
    def __init__(self):
        print("**** BUILDING by {0}!".format(threading.currentThread().getName()))
        self.dht_device = adafruit_dht.DHT22(board.D17)
...

我的main.py看起来像:

import RPi.GPIO as GPIO
from sensor.config.app_config import create_app

if __name__ == '__main__':
    app = create_app()         # builds DHT22Custom inside
    app.run(debug=True)
    print("Cleaning up GPIO before exiting...")
    GPIO.cleanup()

看看我得到了什么有趣的输出:

And look what an interesting output I got:

root@05600e5:/app# python -m sensor.main
**** BUILDING by MainThread!
 * Serving Flask app "FlaskWS" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
 * Restarting with stat
**** BUILDING by MainThread!
Unable to set line 17 to input

MainThread两次初始化了我的对象！怎么样?好吧，如果您查看Flask的run()文档，则会看到以下内容:

The MainThread was initializing my object twice! How was that? Well, if you look at the documentation of Flask's run(), you'll see the following:

If the :attr:`debug` flag is set the server will automatically reload
 for code changes and show a debugger in case an exception happened.

因此，似乎Flask只是重新启动了应用程序或类似的东西.老实说，我不清楚.但是，如果您仅删除debug，则会看到类似以下内容的

So, it seems that Flask just relaunches the application or something like this. Not clear to me, to be honest. But well, if you just remove debug, you'll see something like:

root@05600e5:/app# python -m sensor.main
**** BUILDING by MainThread!
 * Serving Flask app "FlaskWS" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

我希望这会有所帮助.编码愉快！

I hope this helps. Happy coding!

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