从DHT-11温度/湿度传感器到CSV文件的传感器数据(python/ raspberry pi 3)

Question

我有最少的编码经验和相对新手的python，但我正在尝试写一个树莓派(3B+)的python程序，将从DHT-11传感器获得温度和湿度数据，并将其保存到一个.csv文件有3个头:时间戳收集数据，温度值，湿度值。

我已经做了测试，知道我从传感器上得到的读数是正常的。我希望将这些读数以及时间戳放到csv文件中，每个文件都在适当的标题下。我收到一个TypeError: 'NoneType' object is not subscriptable错误。我对如何修复这个错误有点迷茫，因为我对这门语言(和一般的编码)都是新手。这是我在运行程序时在终端中看到的：

pi@rgbpi: ~ Documents $ sudo python3 temp_humidity_csv.py
Beginning cycle 1
Traceback (most recent call last):
File "temp_humidity_csv.py", line 66, in <module> main()
File "temp_humidity_csv.py", line 33, in main add_to_file(data)
File "temp_humidity_csv.py", line 55, in add_to_file data_writer.writerow({'Time': data['timestamp'], 'Temperature': data['temperature'], 'Humidity': data['humidity']})
TypeError: 'NoneType' object is not subscriptable

以下是我的代码：

import RPi.GPIO as GPIO
import csv
import time, datetime
from time import sleep
import Adafruit_DHT
import os.path

#initialize GPIO
GPIO.setwarnings(False)
GPIO.setmode(GPIO.BOARD)
GPIO.cleanup()

#set up DHT sensor
dht_sensor = Adafruit_DHT.DHT11
dht_pin = 7

#global variables
datafile = "/home/pi/Desktop/Temp_Humid.csv"

#main function - will take temp, humidity and timestamp and write to csv every 10s
def main():
    i = 1

    while(1):
        print("Beginning cycle " + str(i))
        data = get_data()
        add_to_file(data)
        sleep(10)
        print("End of cycle " + str(i))
        i = i+1

#get temp and humidity and add to 'data' dictionary
def get_data():
    now = datetime.datetime.now()
    humidity, temp = Adafruit_DHT.read(dht_sensor, dht_pin)
    if humidity is not None and temp is not None:
        data = {'timestamp':str(now.strftime("%Y%m%d_%H-%M-%S")), 'temperature':temp, 'humidity':humidity}
        print(data)
        return(data)

#write temp, humidity and time stamps to csv file
def add_to_file(data):
    if os.path.isfile(datafile): #checks if file exists. if yes, appends values for dictionary under corresponding header in a new line
        with open(datafile, 'a', newline='') as csvfile: 
            fieldnames = ['Time', 'Temperature', 'Humidity']
            data_writer = csv.DictWriter(csvfile, fieldnames=fieldnames, delimiter=' ', quotechar='|', quoting=csv.QUOTE_MINIMAL)

            data_writer.writerow({'Time': data['timestamp'], 'Temperature': data['temperature'], 'Humidity': data['humidity']})
    
    else: #creates file (that has been checked and does not yet exist) and adds headers and values for all 3 keys in dict
        with open(datafile, 'w', newline='') as csvfile: 
            fieldnames = ['Time', 'Temperature', 'Humidity']
            data_writer = csv.DictWriter(csvfile, fieldnames=fieldnames, delimiter=' ', quotechar='|', quoting=csv.QUOTE_MINIMAL)

            data_writer.writeheader()
            data_writer.writerow({'Time': data['timestamp'], 'Temperature': data['temperature'], 'Humidity': data['humidity']})

if __name__ == "__main__":
    main()

Answer 1

如果humidity和temp都不是None，则函数get_data()返回包含数据的字典。否则，它返回None。然后，将get_data()返回的任何内容传递给add_to_file(data)，并将其作为字典使用，虽然它可能是字典，但也可能是None。您可以将main修改为仅当get_data()返回一些实际有用的东西时才调用add_to_file(data) - data不是None。例如：

def main():
    i = 1

    while(1):
        print("Beginning cycle " + str(i))
        data = get_data()
        if data is not None:
            add_to_file(data)

        sleep(10)
        print("End of cycle " + str(i))
        i = i+1

Answer 2

正如kukabadl所说，你的问题是，当你的DHT_11传感器由于线路脆弱而失败时，get_data不会输出任何信息。get_data()函数仅在数据不为None的情况下记录数据。通过在if:语句下面添加else:语句，可以说明数据为空的情况：

else:
    data = {'timestamp':None, 'temperature':None, 'humidity':None}
    print(data)
    return(data)