TypeError: float() argument must be a string or a number, not 'NoneType'

Question

i know that a lot of people have asked related questions but please help me out. I am trying to replicate an opensource temperature control lab i found online. I wanted to run it on Raspberry Pi. This is the error i keep getting:

    Traceback (most recent call last):
  File "/home/pi/Desktop/Python/test_Temperature.py", line 14, in <module>
    print('Temperature 1: ' + str(a.T1) + ' degC')
  File "/home/pi/Desktop/Python/tclab.py", line 26, in T1
    self._T1 = float(self.read('T1'))
TypeError: float() argument must be a string or a number, not 'NoneType'

The code that generates it is this:

import tclab
import numpy as np
import time

try:
    # Connect to Arduino
    a = tclab.TCLab()

    # Get Version
    print(a.version)

    # Temperatures
    print('Temperatures')
    print('Temperature 1: ' + str(a.T1) + ' degC')
    print('Temperature 2: ' + str(a.T2) + ' degC')

    # Turn LED on
    print('LED On')
    a.LED(100)

    # Turn on Heaters (0-100%)
    print('Turn On Heaters (Q1=90%, Q2=80%)')
    a.Q1(90.0)
    a.Q2(80.0)

    # Sleep (sec)
    time.sleep(60.0)

    # Turn Off Heaters
    print('Turn Off Heaters')
    a.Q1(0.0)
    a.Q2(0.0)

    # Temperatures
    print('Temperatures')
    print('Temperature 1: ' + str(a.T1) + ' degC')
    print('Temperature 2: ' + str(a.T2) + ' degC')

# Allow user to end loop with Ctrl-C           
except KeyboardInterrupt:
    # Disconnect from Arduino
    a.Q1(0)
    a.Q2(0)
    print('Shutting down')
    a.close()

# Make sure serial connection still closes when there's an error
except:           
    # Disconnect from Arduino
    a.Q1(0)
    a.Q2(0)
    print('Error: Shutting down')
    a.close()
    raise

I believe the code seeks to communicate with another python file with the below code:

import sys
import time
import numpy as np
try:
    import serial
except:
    import pip
    pip.main(['install','pyserial'])
    import serial
from serial.tools import list_ports

class TCLab(object):

    def __init__(self, port=None, baud=9600):
        if (sys.platform == 'darwin') and not port:
            port = '/dev/ttyACM1'

    def stop(self):
        return self.read('X')

    def version(self):
        return self.read('VER')

    @property
    def T1(self):
        self._T1 = float(self.read('T1'))
        return self._T1

    @property
    def T2(self):
        self._T2 = float(self.read('T2'))
        return self._T2

    def LED(self,pwm):
        pwm = max(0.0,min(100.0,pwm))/2.0
        self.write('LED',pwm)
        return pwm

    def Q1(self,pwm):
        pwm = max(0.0,min(100.0,pwm)) 
        self.write('Q1',pwm)
        return pwm

    def Q2(self,pwm):
        pwm = max(0.0,min(100.0,pwm)) 
        self.write('Q2',pwm)
        return pwm

    # save txt file with data and set point
    # t = time
    # u1,u2 = heaters
    # y1,y2 = tempeatures
    # sp1,sp2 = setpoints
    def save_txt(self,t,u1,u2,y1,y2,sp1,sp2):
        data = np.vstack((t,u1,u2,y1,y2,sp1,sp2))  # vertical stack
        data = data.T                 # transpose data
        top = 'Time (sec), Heater 1 (%), Heater 2 (%), ' \
          + 'Temperature 1 (degC), Temperature 2 (degC), ' \
          + 'Set Point 1 (degC), Set Point 2 (degC)' 
        np.savetxt('data.txt',data,delimiter=',',header=top,comments='')

    def read(self,cmd):
        cmd_str = self.build_cmd_str(cmd,'')
        try:
            self.sp.write(cmd_str.encode())
            self.sp.flush()
        except Exception:
            return None
        return self.sp.readline().decode('UTF-8').replace("\r\n", "")

    def write(self,cmd,pwm):       
        cmd_str = self.build_cmd_str(cmd,(pwm,))
        try:
            self.sp.write(cmd_str.encode())
            self.sp.flush()
        except:
            return None
        return self.sp.readline().decode('UTF-8').replace("\r\n", "")

    def build_cmd_str(self,cmd, args=None):
        """
        Build a command string that can be sent to the arduino.

        Input:
            cmd (str): the command to send to the arduino, must not
                contain a % character
            args (iterable): the arguments to send to the command
        """
        if args:
            args = ' '.join(map(str, args))
        else:
            args = ''
        return "{cmd} {args}\n".format(cmd=cmd, args=args)

    def close(self):
        try:
            self.sp.close()
            print('Arduino disconnected successfully')
        except:
            print('Problems disconnecting from Arduino.')
            print('Please unplug and reconnect Arduino.')
        return True

I do not know my around python codes yet so a very clear 'for dummy class' explanation of the solution would really help. Thanks guys.

Solution

This is the read() function:

def read(self,cmd):
    cmd_str = self.build_cmd_str(cmd,'')
    try:
        self.sp.write(cmd_str.encode())
        self.sp.flush()
    except Exception:
        return None
    return self.sp.readline().decode('UTF-8').replace("\r\n", "")

One of the things it can return is None as you can see in the return None line. If that happens, then your line:

float(self.read('T1'))

will fail, because it will try to convert None into a float, and that gives the error you're getting.

Comments

[Acccumulation]

Do you understand the difference between a class and an object?

[Tochukwu Anyaduba]

maybe not in detail as a Pro should but i fairly understand the concept

[Tochukwu Anyaduba]

Thank you so much for your prompt response. Please, how do i correct it?

[Tochukwu Anyaduba]

i changed None to 0. The program ran but only gave me the value 0. Please how do i effectively correct this?

[nosklo]

@TochukwuAnyaduba that try/except construct is to catch errors in the self.sp.write line. If some error occurs, the error is silenced and you get None (now 0 with your edits) instead. In other words, you have some kind of error writing to the serial port, and the error is being silenced by the code, returning zero instead. Your device probably is not connected to the serial port or you have some other problem. I don't know if the code is complete but I can't find where self.sp is defined at all so maybe you're missing the definition?

[Tochukwu Anyaduba]

Thank you once again. you are very correct. this is not the complete code. The files can be found here: github.com/jckantor/TCLab/tree/master/tclab

[Tochukwu Anyaduba]

I ran the codes on Windows, it worked fine, but just not working on Raspberry pi

[Tochukwu Anyaduba]

I finally got the code to work. Apparently, I was trying to communicate via serial while Arduino Leonardo was connected to my Pi via USB, I also was not using Arduino IDE meant for Linux so it kept crashing. Now everything runs smoothly. There is no problem with the code