Error while closing the python serial port - python-2.7

Question

" i am trying to read data from the serial connection and doing some stuff if it matches my string but its giving me errors when i close the serial connection port"
" for some reason i do not see this error if i use the serial.readline() method "
import time
import serial
from Queue import Queue
from threading import Thread
class NonBlocking:
def __init__(self, serial_connection, radio_serial_connection):
self._s = serial_connection
self._q = Queue()
self.buf = bytearray()
def _populateQueue(serial_connection, queue):
if type(serial_connection) == str:
return
self.s = serial_connection
while True:
i = self.buf.find(b"\n")
if i >= 0:
r = self.buf[:i + 1]
self.buf = self.buf[i + 1:]
queue.put(r)
while True:
i = max(1, min(2048, self.s.in_waiting))
data = self.s.read(i)
i = data.find(b"\n")
if i >= 0:
r = self.buf + data[:i + 1]
self.buf[0:] = data[i + 1:]
a = r.split('\r\n')
for item in a:
if item:
queue.put(item)
else:
self.buf.extend(data)
self._t = Thread(target=_populateQueue, args=(self._s, self._q))
self._t.daemon = True
self._t.start()
def read_all(self, timeout=None):
data = list()
if self._q.empty():
pass
while not self._q.empty():
data.append(self._q.get(block=timeout is not None, timeout=timeout))
return data
class SerialCommands:
def __init__(self, port, baudrate):
self.serial_connection = serial.Serial(port, baudrate)
self.queue_data = NonBlocking(self.serial_connection, '')
def read_data(self):
returned_info = self.queue_data.read_all()
return returned_info
def close_q(self):
self.serial_connection.close()
class qLibrary:
def __init__(self):
self.q = None
self.port = None
def close_q_connection(self):
self.q.close_q()
def establish_connection_to_q(self, port, baudrate=115200, delay=2):
self.delay = int(delay)
self.port = port
try:
if not self.q:
self.q = SerialCommands(self.port, int(baudrate))
except IOError:
raise AssertionError('Unable to open {0}'.format(port))
def verify_event(self, data, timeout=5):
timeout = int(timeout)
data = str(data)
# print data
while timeout:
try:
to_analyze = self.q.read_data()
for item in to_analyze:
print "item: ", item
if str(item).find(str(data)) > -1:
print "Found data: '{0}' in string: '{1}'".format(data, item)
except:
pass
time.sleep(1)
timeout -= 1
if __name__ == '__main__':
q1 = qLibrary()
q1.establish_connection_to_q('COM5')
q1.verify_event("ATE")
q1.close_q_connection()
" i expect the code to close the serial connection without any exceptions or errors "
the output is
Exception in thread Thread-1:
Traceback (most recent call last):
File "C:\Python27\Lib\threading.py", line 801, in __bootstrap_inner
self.run()
File "C:\Python27\Lib\threading.py", line 754, in run
self.__target(*self.__args, **self.__kwargs)
File "C:/Program Files (x86)/serialtest1.py", >line 27, in _populateQueue
data = self.s.read(i)
File "C:\Program Files (x86)\venv\lib\site->packages\serial\serialwin32.py", line 283, in read
ctypes.byref(self._overlapped_read))
TypeError: byref() argument must be a ctypes instance, not 'NoneType'

Answer 1

If you define your serial port with no timeout it will get the default setting timeout=None which means when you call serial.read(x) the code will block until you read x bytes.
If you never get those x bytes your code will get stuck in there waiting forever, or at least until you receive more data on the buffer to get the total number of bytes received equal to x.
If you mix that up with threading, I'm afraid you are quite likely closing the port while you are trying to read.
You can probably fix this issue just defining a sensible read timeout on your port or changing the way you read. The general advice is to set a timeout that works for your application and read at least the maximum number of bytes you expect. Reading your code, that seems to be what you wanted to do. If so, you forgot to set the timeout.
If you have a reason not to set a timeout or you want to keep your reading routine as it is, you can make your code work if you cancel reading before closing. You can do that with serial.cancel_read()