Python script makes AssertionError when trying to MariaDB

Question

I have this piece of code that collects data from a HAT connected to a Raspberry. When run it gives this error:

[51.57, 22.30, 1002.01]
Traceback (most recent call last):
  File "dbWriter.py", line 45, in <module>
    write2DB(record)
  File "dbWriter.py", line 26, in write2DB
    assert len(values) == 3
AssertionError

I am by no means a programmer, i just fiddle around. It is meant to save 'record' to a database, which is then read and updated in realtime on an apache2 server. All help appreciated.

import mysql.connector
from itertools import repeat
import sys
import bme680
import time

try:
   sensor = bme680.BME680(bme680.I2C_ADDR_PRIMARY)
except IOError:
   sensor = bme680.BME680(bme680.I2C_ADDR_SECONDARY)

sensor.set_humidity_oversample(bme680.OS_2X)
sensor.set_pressure_oversample(bme680.OS_4X)
sensor.set_temperature_oversample(bme680.OS_8X)
sensor.set_filter(bme680.FILTER_SIZE_3)

mydb = mysql.connector.connect(
    host='localhost',
    user='pi',
    passwd='pass',
    database='weatherDB'
)
mycursor = mydb.cursor()

def write2DB(values):
    assert len(values) == 3
    sqlText = '''INSERT INTO data(humidity, temperature, pressure) VALUES({},{}, })'''.format(values[0], values[1], values[2])
    mycursor.execute(sqlText)
    mydb.commit()

for _ in repeat(None):
   sensor.get_sensor_data()
   output_humi = '{0:.2f}'.format(
       sensor.data.humidity)
   output_temp = '{0:.2f}'.format(
       sensor.data.temperature)
   output_pres = '{0:.2f}'.format(
       sensor.data.pressure)
   record = []
   record = ('[' + (output_humi) + ', ' + (output_temp) + ', ' + (output_pres) + ']')
   print(record)
   write2DB(record)
   time.sleep(10)
   pass

Answer 1

You have:

record = ('[' + (output_humi) + ', ' + (output_temp) + ', ' + (output_pres) + ']')

record evaluates to a single string, not a list of 3 elements and hence your exception.

Change the above to:

record = [output_humi, output_temp, output_pres]

You are also missing a { in your format specification. It should be:

sqlText = '''INSERT INTO data(humidity, temperature, pressure) VALUES({},{}, {})'''.format(values[0], values[1], values[2])

An alternative would be to use a prepared statement:

sqlText = 'INSERT INTO data(humidity, temperature, pressure) VALUES(%s, %s, %s)'
mycursor.execute(sqlText, values)

In the above case you will be passing actual strings as the values. I don't know how the columns are defined, but no matter. If they are defined as floating point or decimal values, the strings will be converted to the correct type.