使用 python 的 pymysql 数据库存储错误

Question

i am having a error in this program, i am trying to store my output in a database collected from temperature sensor using arduino program

python code

import serial
import pymysql

device = /dev/ttyACM0'
arduino = serial.Serial(device,9600)

data  = arduino.readline()
print (data)

connection = pymysql.conect("localhost","pi","","temperature_db) or die("cant connect to database")

print (connection)

with connection:
cursor = connection .cursor 
cursor.execute("INSERT INTO tempLog (Temperature) VALUES (%s)" %(data))
connection.commit()
connection.execute()

this is how I have created my database.

and this is what i have written in my arduino code

and this is the error I received for python code

can anyone please help me to solve this issue and explain why I had that error and how it was fixed?

Answer 1

Try this:

cursor.execute(f"INSERT INTO tempLog (Temperature) VALUES ({data.decode('utf-8').strip()}" )

Explanation

There are two issues that need to be corrected:

• The byte variable data (b'Temp: 26 C\r\n') needs to be converted to a string and whitespaces ('r\n') stripped off using for example data.decode("utf-8").strip()

• The sql insert statement expect a quoted string value like this VALUES ("Temp: 26C") .

1. Example of the different steps using Python

#
# The current sql insert look like this. Notice the value type
#
>>> "INSERT INTO tempLog (Temperature) VALUES (%s)" %(data)
"INSERT INTO tempLog (Temperature) VALUES (b'Temp: 26C\\r\\n')"

#
# Convert data to a string and strip white spaces
#
>>> data = data.decode("utf-8").strip()
>>> "INSERT INTO tempLog (Temperature) VALUES (%s)" %(data)
'INSERT INTO tempLog (Temperature) VALUES (Temp: 26C)'

#
# Finaly add quotes to VALUES to pass data as a string
#
>>> "INSERT INTO tempLog (Temperature) VALUES (\"%s\")" %(data)
'INSERT INTO tempLog (Temperature) VALUES ("Temp: 26C")'

#
# Final suggestion using python f-string
#
cursor.execute(f"INSERT INTO tempLog (Temperature) VALUES ({data.decode('utf-8').strip()}" )

2. Your code with the suggested modifications.

import serial
import pymysql

device = /dev/ttyACM0'
arduino = serial.Serial(device,9600)

data  = arduino.readline()

data = data.decode("utf-8").strip() # Convert to str and strip whitespaces
print (data)

connection = pymysql.connect("localhost","pi","","temperature_db") or die("cant connect to database")

print (connection)

with connection:
    cursor = connection.cursor()

    sql = ("INSERT INTO tempLog (Temperature) VALUES (\"%s\");" % data)
    print(f"sql: {sql}") 

    try:
        cursor.execute(sql)
        connection.commit()
    except Exception as e:
        print(e)