将 python 队列模块从 python2 转换为 python3

Question

I have a logging script that will log serial output from multiple devices in a queue of serial terms into stdout. In python 2.7 the script worked as intended. However upon converting the script to python3. I noticed that after I converted the queue module to its python3 form, my script started printing out empty lines in addition to the regular expected output. Could someone explain what the cause of this is and any best practice to fix this?

#!/usr/bin/env python3
# -*- coding: UTF-8 -*-

import serial
import sys
import threading
from datetime import datetime
import glob
import time
import os
import termcolor as tc
import queue

__version__ = 2.0

COLOR = True
# Available colors
#   blue, yellow, green, cyan,
#   magenta, white, red, grey,
#   light_grey, on_red

# Add light grey to the colors dictionary
tc.COLORS['light_grey'] = 38
# Add a highlight color
tc.COLORS['on_red'] = 41

TIMEOUT = 0.05 # seconds

DEVS = []
usb_devices = []
speaker_types = ['Tx', 'Rx-FL', 'Rx-FR', 'Rx-Center', 'Rx-Subwoofer']

stamp = time.strftime("%Y:%m:%d-%H:%M:%S")

def serial_ports():
    if sys.platform.startswith('win'):
        ports = ['COM%s' % (i + 1) for i in range(256)]
    elif sys.platform.startswith('linux') or sys.platform.startswith('cygwin'):
        ports = glob.glob('/dev/tty[A-Za-z]*')
    elif sys.platform.startswith('darwin'):
        ports = glob.glob('/dev/tty.*')
    else:
        raise EnvironmentError('Unsupported platform')
    result = []
    for port in ports:
        try:
            s = serial.Serial(port)
            s.close()
            result.append(port)
        except (OSError, serial.SerialException):
            pass
    result.reverse()
    print("Ports: " + str(result))
    pattern = 'USB'
    usb_devices = [string for string in result if pattern in string]
    return usb_devices
    
def add_device(position):    
    name = speaker_types[position]
    return name


class SerialTerm(object):
    """A serial terminal that runs in its own thread"""
    def __init__(self, name, port, timeout, queue, baudrate=2000000, color=None):
        self.name = name
        self.port = port
        self.timeout = timeout
        self.queue = queue
        self.baudrate = baudrate
        self.color = color

        self.receiver_thread = None
        self.alive = None

        self.serial = serial.serial_for_url(
            self.port,
            timeout=self.timeout,
            baudrate=self.baudrate)

    def start(self):
        """Starts the terminal thread"""
        self.alive = True
        self.receiver_thread = threading.Thread(target=self.reader)
        self.receiver_thread.setDaemon(True)
        self.receiver_thread.start()
        #self.reset()

    def stop(self):
        """Stops the terminal thread"""
        self.alive = False
        self.receiver_thread.join()

    def reader(self):
        """Reads data from the associated serial port and puts the data in a
        queue"""
        while self.alive:
            now = datetime.utcnow()
            line = self.serial.readline()
            if line != "": 
                output_str = f"{now.time().isoformat()[:12]}(UTC) {self.name}> {line}"

                if COLOR and (self.color is not None):
                    output_str = tc.colored(output_str, self.color)
                    
                self.queue.put(output_str)


    def join(self):
        """Waits until thread terminates"""
        self.receiver_thread.join()
        
def main():
    print("Getting Devices")
    dev = serial_ports()
    
    position = 0
    name = ''

    for d in dev:
        name = add_device(position)
        DEVS.append({'port':dev[position], 'name':name, 'color':'white'})
        position += 1
        
    print('DEVS: ' + str(DEVS))
    
    """Round robin serial polling"""
    sys.stdout.write("v{}\n".format(__version__))
    sys.stdout.flush()
    que = queue.Queue()

    terms = []
    for dev in DEVS:
        terms.append(
            SerialTerm(
                name=dev['name'],
                port=dev['port'],
                color=dev['color'],
                timeout=TIMEOUT,
                queue=que))

    for term in terms:
        term.start()

    try:
        while True:
            try:
                # The queue.get method needs a timeout or KeyboardInterrupt won't ever raise.
                sys.stdout.write(que.get(timeout=60) + "\n")
                sys.stdout.flush()
            except queue.Empty: 
                pass
    except KeyboardInterrupt:
        sys.stderr.write("\nQuitting\n")
        for term in terms:
           term.stop()
           term.join()
           sys.exit()
           sys.stdout.flush()
    except:
        raise

if __name__ == '__main__':
    main()

Here is an example of the bad output python3 has been giving me. It would just spam these empty lines indefinitely in addition to any normal printout that is displayed.

00:53:00.859(UTC) Tx> b''
00:53:00.909(UTC) Tx> b''
00:53:00.960(UTC) Tx> b''
00:53:01.010(UTC) Tx> b''
00:53:01.061(UTC) Tx> b''
00:53:01.111(UTC) Tx> b''
00:53:00.859(UTC) Tx> b'Expected Printout'
00:53:00.909(UTC) Tx> b''
00:53:00.960(UTC) Tx> b''
00:53:01.010(UTC) Tx> b''
00:53:01.061(UTC) Tx> b''
00:53:01.111(UTC) Tx> b''

Answer 1

the bug is here:

            line = self.serial.readline()
            if line != "": 
                output_str = f"{now.time().isoformat()[:12]}(UTC) {self.name}> {line}"

                if COLOR and (self.color is not None):
                    output_str = tc.colored(output_str, self.color)
                    
                self.queue.put(output_str)

self.serial.readline() returns a bytes object. As a result, it will not compare equal to str objects such as "" , so empty lines are no longer filtered out.

To fix it, you will need to convert the return value of self.serial.readline() to str with bytes.decode

See this guide for more details about the changes to strings made in python 3, and how to properly port python 2 code.