Problems with python code

Question

Below is a little code that I have written in python that is scheduled on a crontab to run every 15 minutes. It is supposed to check the temperature of the CPU on my raspberry pi, and text me asking what to do if the temperature is above 45 degrees Celsius. I know I am receiving the correct temperature value because it prints to the screen as a number. However, I seem to get a text message every 15 minutes stating its temperature even thought it is below 45 degrees. I know the error must be in my conditional somewhere, but I am new to python syntax and can't figure it out. Ive tried comparing to both 45 and 45.0 using both > and >=.

import os
import smtplib
import sys

# Return CPU temperature as a character string                                      
def getCPUtemperature():
    res = os.popen('vcgencmd measure_temp').readline()
    return(res.replace("temp=","").replace("'C\n",""))

# CPU informatiom
CPU_temp = getCPUtemperature()

if CPU_temp > 45.0:
    fromaddr = '[email protected]'
    toaddrs  = '[email protected]'
    msg = 'My current CPU temperature is %s degrees. Should I shutdown?' % (CPU_temp)
    # Credentials (if needed)  
    username = 'xxxxxxxxxx'
    password = 'xxxxxxxxxx'
    # The actual mail send  
    server = smtplib.SMTP('smtp.gmail.com:587')
    server.starttls()
    server.login(username,password)
    server.sendmail(fromaddr, toaddrs, msg)
    server.quit()
    sys.exit()
else:
    sys.exit()

Try casting CPU_temp as a float like so if float(CPU_temp) > 45.0. If you're returning it as a string, it might need an explicit cast. — Charles Clayton
– Charles Clayton, Commented Apr 5, 2014 at 0:56

Ruben Bermudez · Accepted Answer · 2014-04-05 00:57:27Z

You can't compare a string (returned by getCPUtemperature) with a float 45.0, try casting the string to float:

import os
import smtplib
import sys

# Return CPU temperature as a character string                                      
def getCPUtemperature():
    res = os.popen('vcgencmd measure_temp').readline()
    return(res.replace("temp=","").replace("'C\n",""))

# CPU informatiom
CPU_temp = getCPUtemperature()

if float(CPU_temp) > 45.0:
    fromaddr = '[email protected]'
    toaddrs  = '[email protected]'
    msg = 'My current CPU temperature is %s degrees. Should I shutdown?' % (CPU_temp)
    # Credentials (if needed)  
    username = 'xxxxxxxxxx'
    password = 'xxxxxxxxxx'
    # The actual mail send  
    server = smtplib.SMTP('smtp.gmail.com:587')
    server.starttls()
    server.login(username,password)
    server.sendmail(fromaddr, toaddrs, msg)
    server.quit()
    sys.exit()
else:
    sys.exit()

shaktimaan · Accepted Answer · 2014-04-05 00:58:35Z

0

Depends on what getCPUtemperature() returns. If the method returns a string, say "15", the conditional will be true.

>>> "15" > 45.0
>>> True

>>> "64" > 45.0
>>> True

Cast the return value of getCPUtemperature() to float before the if condition.

answered Apr 5, 2014 at 0:58

shaktimaan

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Comments

Charles Clayton · Accepted Answer · 2014-04-05 00:59:20Z

0

CPU_temp needs to be explicitly cast as a float because you're returning a string. You can either convert it like CPU_temp = float(CPU_temp) or just do the cast in the comparison. Here's a trace explanation of what's happening:

>>> CPU_temp = "53.1"
>>> if CPU_temp > 45.0:
    print("True")
TypeError: unorderable types: str() > float()

>>> if float(CPU_temp) > 45.0:
    print("True")
True

answered Apr 5, 2014 at 0:59

Charles Clayton

18.2k15 gold badges94 silver badges123 bronze badges

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