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

Question

I have minimal coding experience and am relatively new to python, but am trying to write a python program for raspberry pi (3B+) that will get temperature and humidity data from the DHT-11 sensor and save it to a.csv file with 3 headers: timestamp of when data was collected, temperature value, humidity value.

I have already done testing to know that I am getting readings from the sensor just fine. I want to get those readings, along with timestamps, into a csv file with each under the appropriate header. I am getting a TypeError: 'NoneType' object is not subscriptable error. I'm a little lost on how I can fix the error since I'm new to the language (and coding in general). This is what I'm seeing in terminal when I run the program:

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

The following is my code:

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

Function get_data() returns dictionary with data if neither humidity nor temp are None . Otherwise it returns None . Then you pass whatever get_data() returned to add_to_file(data) where you are using that as if it were a dictionary which it might be but it also might be None . You can modify main to only call add_to_file(data) if get_data() returned something actually useful - data is not None. For example like this:

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

As kukabadl said, your problem is that when your DHT_11 sensor fails due to the wiring being flimsy, get_data outputs None. your get_data() function only records data in case where data isn't None. By adding an else: statement below your if: statement you can account for cases in which data is None:

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