- Python Timeout Example
- Python Serial Write Timeout Exception
- Python Serial Write Timeout In C
- Python Serial Readline Timeout
Do specify a timeout when opening the serial port otherwise it could block forever if no newline character is received. Also note that readlines only works with a timeout. Readlines depends on having a timeout and interprets that as EOF (end of file). It raises an exception if the port is not opened correctly.
Do specify a timeout when opening the serial port otherwise it could block forever if no newline character is received. Also note that readlines only works with a timeout. Readlines depends on having a timeout and interprets that as EOF (end of file). It raises an exception if the port is not opened correctly. Import serial send = serial.Serial(port = 'COM4', baudrate = 9600, timeout = 0) send.write('Hello') send.close When starting the sender script, the receiver script gets the sent message (So communication is clearly established) but the sender script immediately ends with an error. Access to the port settings through Python properties. Support for different byte sizes, stop bits, parity and flow control with RTS/CTS and/or Xon/Xoff. Working with or without receive timeout. File like API with “read” and “write” (“readline” etc. Also supported). The files in this package are 100% pure Python.
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Comments
commented Oct 4, 2015
When I set a timeout like this: pyserial just retries reads like this: I need to be able to know, when the read has timed out to resend my last message. Magnetic resistance exercise bike reviews. Please raise a TimeoutError, so I can use pyserial like this: I think that it is unpythonic to silently drop errors like a timeout. When a user of pyserial invokes a read(), the expected outcome is that it returns the data that has been read. So hitting the timeout is an error. |
commented Oct 4, 2015
I found a workaround of using threads that communicate over queues: |
commented Oct 4, 2015
You can detect that there was a timeout by checking the length of returned bytes versus the number of bytes requested. It is more like an EOF in Python, rather than a timeout error. That is also how some protocols are using the timeout, as packet delimiter. An exception would be inconvenient in many cases. E.g. consider reading more than one byte but fewer arrive, the timeout strikes. Then you'd still expect to get the bytes, but how? Attached to the exception? Driver hours spreadsheet online. Probably not where most people would expect to find data. When they would be returned with the current read() call, then the timeout exception would need be raised in the next call which is certainly also not what one would expect. |
commented Oct 6, 2015
Thanks for your reply, @zsquareplusc. Checking the length of the returned bytes did not work for me. console.read() timed out repeatedly and there were never any bytes returned.If I requested a specified number of bytes with a timeout, I would either expect that exact number of bytes or an exception. I am not sure if it would also be OK to return all bytes that have been read up to the timeout. That would definitely need to be documented and users would need to check whether the received data is complete. I think there is little value in aborted data, because the timeout can strike at any given instance, so users would need to program every eventuality. In practice this means to handle as many cases as characters requested. Restarting the communication should be easier to program in most cases. |
closed this Oct 20, 2015
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Python Timeout Example
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zsquarepluscstyle: use .format() instead of % formatting3debab2Jun 20, 2016
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Python Serial Write Timeout In C
#! /usr/bin/env python |
# |
# This file is part of pySerial - Cross platform serial port support for Python |
# (C) 2001-2015 Chris Liechti <[email protected]> |
# |
# SPDX-License-Identifier: BSD-3-Clause |
'' |
Some tests for the serial module. |
Part of pyserial (http://pyserial.sf.net) (C)2001-2015 [email protected] |
Intended to be run on different platforms, to ensure portability of |
the code. |
For all these tests a simple hardware is required. |
Loopback HW adapter: |
Shortcut these pin pairs: |
TX <-> RX |
RTS <-> CTS |
DTR <-> DSR |
On a 9 pole DSUB these are the pins (2-3) (4-6) (7-8) |
'' |
import unittest |
import threading |
import time |
import sys |
import serial |
# on which port should the tests be performed: |
PORT='loop://' |
# indirection via bytearray b/c bytes(range(256)) does something else in Pyhton 2.7 |
bytes_0to255 =bytes(bytearray(range(256))) |
defsegments(data, size=16): |
for a inrange(0, len(data), size): |
yield data[a:a + size] |
classTest4_Nonblocking(unittest.TestCase): |
''Test with timeouts'' |
timeout =0 |
defsetUp(self): |
self.s = serial.serial_for_url(PORT, timeout=self.timeout) |
deftearDown(self): |
self.s.close() |
deftest0_Messy(self): |
''NonBlocking (timeout=0)'' |
# this is only here to write out the message in verbose mode |
# because Test3 and Test4 print the same messages |
deftest1_ReadEmpty(self): |
''timeout: After port open, the input buffer must be empty'' |
self.assertEqual(self.s.read(1), b'', 'expected empty buffer') |
deftest2_Loopback(self): |
''timeout: each sent character should return (binary test). |
this is also a test for the binary capability of a port.'' |
for block in segments(bytes_0to255): |
length =len(block) |
self.s.write(block) |
# there might be a small delay until the character is ready (especially on win32) |
time.sleep(0.05) |
self.assertEqual(self.s.in_waiting, length, 'expected exactly {} character for inWainting()'.format(length)) |
self.assertEqual(self.s.read(length), block) #, 'expected a %r which was written before' % block) |
self.assertEqual(self.s.read(1), b'', 'expected empty buffer after all sent chars are read') |
deftest2_LoopbackTimeout(self): |
''timeout: test the timeout/immediate return. |
partial results should be returned.'' |
self.s.write(b'HELLO') |
time.sleep(0.1) # there might be a small delay until the character is ready (especially on win32 and rfc2217) |
# read more characters as are available to run in the timeout |
self.assertEqual(self.s.read(10), b'HELLO', 'expected the 'HELLO' which was written before') |
self.assertEqual(self.s.read(1), b'', 'expected empty buffer after all sent chars are read') |
classTest3_Timeout(Test4_Nonblocking): |
''Same tests as the NonBlocking ones but this time with timeout'' |
timeout =1 |
deftest0_Messy(self): |
''Blocking (timeout=1)'' |
# this is only here to write out the message in verbose mode |
# because Test3 and Test4 print the same messages |
classSendEvent(threading.Thread): |
def__init__(self, serial, delay=3): |
threading.Thread.__init__(self) |
self.serial = serial |
self.delay = delay |
self.x = threading.Event() |
self.stopped =0 |
self.start() |
defrun(self): |
time.sleep(self.delay) |
self.x.set() |
ifnotself.stopped: |
self.serial.write(b'E') |
self.serial.flush() |
defisSet(self): |
returnself.x.isSet() |
defstop(self): |
self.stopped =1 |
self.x.wait() |
classTest1_Forever(unittest.TestCase): |
''Tests a port with no timeout. These tests require that a |
character is sent after some time to stop the test, this is done |
through the SendEvent class and the Loopback HW.'' |
defsetUp(self): |
self.s = serial.serial_for_url(PORT, timeout=None) |
self.event = SendEvent(self.s) |
deftearDown(self): |
self.event.stop() |
self.s.close() |
deftest2_ReadEmpty(self): |
''no timeout: after port open, the input buffer must be empty (read). |
a character is sent after some time to terminate the test (SendEvent).'' |
c =self.s.read(1) |
ifnot (self.event.isSet() and c b'E'): |
self.fail('expected marker (evt={!r}, c={!r})'.format(self.event.isSet(), c)) |
classTest2_Forever(unittest.TestCase): |
''Tests a port with no timeout'' |
defsetUp(self): |
self.s = serial.serial_for_url(PORT, timeout=None) |
deftearDown(self): |
self.s.close() |
deftest1_inWaitingEmpty(self): |
''no timeout: after port open, the input buffer must be empty (in_waiting)'' |
self.assertEqual(self.s.in_waiting, 0, 'expected empty buffer') |
deftest2_Loopback(self): |
''no timeout: each sent character should return (binary test). |
this is also a test for the binary capability of a port.'' |
for block in segments(bytes_0to255): |
length =len(block) |
self.s.write(block) |
# there might be a small delay until the character is ready (especially on win32 and rfc2217) |
time.sleep(0.05) |
self.assertEqual(self.s.in_waiting, length) #, 'expected exactly %d character for inWainting()' % length) |
self.assertEqual(self.s.read(length), block) #, 'expected %r which was written before' % block) |
self.assertEqual(self.s.in_waiting, 0, 'expected empty buffer after all sent chars are read') |
classTest0_DataWires(unittest.TestCase): |
''Test modem control lines'' |
defsetUp(self): |
self.s = serial.serial_for_url(PORT) |
deftearDown(self): |
self.s.close() |
deftest1_RTS(self): |
''Test RTS/CTS'' |
self.s.rts =False |
time.sleep(1.1) |
self.assertTrue(notself.s.cts, 'CTS -> 0') |
self.s.rts =True |
time.sleep(1.1) |
self.assertTrue(self.s.cts, 'CTS -> 1') |
deftest2_DTR(self): |
''Test DTR/DSR'' |
self.s.dtr =False |
time.sleep(1.1) |
self.assertTrue(notself.s.dsr, 'DSR -> 0') |
self.s.dtr =True |
time.sleep(1.1) |
self.assertTrue(self.s.dsr, 'DSR -> 1') |
deftest3_RI(self): |
''Test RI'' |
self.assertTrue(notself.s.ri, 'RI -> 0') |
classTest_MoreTimeouts(unittest.TestCase): |
''Test with timeouts'' |
defsetUp(self): |
# create an closed serial port |
self.s = serial.serial_for_url(PORT, do_not_open=True) |
deftearDown(self): |
self.s.reset_output_buffer() |
self.s.flush() |
#~ self.s.write(serial.XON) |
self.s.close() |
# reopen.. some faulty USB-serial adapter make next test fail otherwise.. |
self.s.timeout =1 |
self.s.xonxoff =False |
self.s.open() |
self.s.read(3000) |
self.s.close() |
deftest_WriteTimeout(self): |
''Test write() timeout.'' |
# use xonxoff setting and the loop-back adapter to switch traffic on hold |
self.s.port =PORT |
self.s.write_timeout =1.0 |
self.s.xonxoff =True |
self.s.open() |
self.s.write(serial.XOFF) |
time.sleep(0.5) # some systems need a little delay so that they can react on XOFF |
t1 = time.time() |
self.assertRaises(serial.SerialTimeoutException, self.s.write, b'timeout please'*200) |
t2 = time.time() |
self.assertTrue(0.9<= (t2 - t1) <2.1, 'Timeout not in the given interval ({})'.format(t2 - t1)) |
if__name__'__main__': |
sys.stdout.write(__doc__) |
iflen(sys.argv) >1: |
PORT= sys.argv[1] |
sys.stdout.write('Testing port: {!r}n'.format(PORT)) |
sys.argv[1:] = ['-v'] |
# When this module is executed from the command-line, it runs all its tests |
unittest.main() |
Python Serial Readline Timeout
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