Develop Reference

pygatt NotificationTimeout: None

I try to read characteristic data out of an BLE based Sensor. Therefore i use the pygatt module
import pygatt
adapter = pygatt.GATTToolBackend()
try:
adapter.start()
device = adapter.connect("2B:01:56:6C:F4:E6")
value= device.char_read("00007502-0000-1000-8000-00805f9b34fb")
finally:
adapter.stop()
Everytime i try to run this in my Linux console (with Python 2.7.16) i get an error :
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/pi/.local/lib/python2.7/site-packages/pygatt/backends/gatttool/device.py", line 17, in wrapper
return func(self, *args, **kwargs)
File "/home/pi/.local/lib/python2.7/site-packages/pygatt/backends/gatttool/device.py", line 40, in char_read
return self._backend.char_read(self, uuid, *args, **kwargs)
File "/home/pi/.local/lib/python2.7/site-packages/pygatt/backends/gatttool/gatttool.py", line 50, in wrapper
return func(self, *args, **kwargs)
File "/home/pi/.local/lib/python2.7/site-packages/pygatt/backends/gatttool/gatttool.py", line 593, in char_read
self.sendline('char-read-uuid %s' % uuid)
File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__
self.gen.next()
File "/home/pi/.local/lib/python2.7/site-packages/pygatt/backends/gatttool/gatttool.py", line 191, in event
self.wait(event, timeout)
File "/home/pi/.local/lib/python2.7/site-packages/pygatt/backends/gatttool/gatttool.py", line 157, in wait
raise NotificationTimeout()
pygatt.exceptions.NotificationTimeout: None
I am completely lost on this error. Do you know how to fix this ?
Any help on this much appreciated. Thanks in advance...

Since I was facing the same problem and nobody out there seemed to have this problem...
Well, the problem was that the requested UUID characteristic didn't exist/was invalid. Make sure that you've typed it right or that you haven't clipped some part off when copying from putty or similar (Totally not speaking from experience! Of course!)
If you are pasting a characteristic UUID from the internet or a similar device, maybe your device don't have this UUID.
OR
This could (not tested, but should make sense) also happen if you write to an UUID which is non-writeable (read-only/subscribe-only).
If you're sure that everything is right and that you have triple-checked the UUID with a dedicated sniffer or simply a BLE Scanner on your Phone, then the device is probably closing the connection too fast.
TROUBLESHOOTING:
You can manually connect with the device and issue commands using:
gatttool -I
When you are inside the program, type:
connect aa:bb:cc:dd:ee:ff
And then, before the connection closes:
char-read-uuid xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
and analyse what happens. If it works there, it should also work in python.

How to solve "control message failed, win error: A device which does not exist was specified" error PyUSB

I'm trying to connect a POS receipt printer to python and have been using python-escpos to do so. I'm running windows 10.
My code in my file 'print.py' is:
from escpos.printer import Usb
p = Usb(0x0456,0x0808)
p.text('Hello World\n')
but when i run it i get the following error log:
Traceback (most recent call last):
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 223, in get_interface_and_endpoint
return self._ep_info[endpoint_address]
KeyError: 1
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "print.py", line 5, in <module>
p.text('Hello World\n')
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\escpos\escpos.py", line 437, in text
self._raw(txt.encode())
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\escpos\printer.py", line 73, in _raw
self.device.write(self.out_ep, msg, self.timeout)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 940, in write
intf, ep = self._ctx.setup_request(self, endpoint)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 102, in wrapper
return f(self, *args, **kwargs)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 215, in setup_request
intf, ep = self.get_interface_and_endpoint(device, endpoint_address)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 102, in wrapper
return f(self, *args, **kwargs)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 225, in get_interface_and_endpoint
for intf in self.get_active_configuration(device):
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 102, in wrapper
return f(self, *args, **kwargs)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\core.py", line 239, in get_active_configuration
bConfigurationValue=self.backend.get_configuration(self.handle)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\backend\libusb0.py", line 510, in get_configuration
100)
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\backend\libusb0.py", line 593, in ctrl_transfer
timeout
File "C:\Users\Harry\AppData\Local\Programs\Python\Python36-32\lib\site-packages\usb\backend\libusb0.py", line 431, in _check
raise USBError(errmsg, ret)
usb.core.USBError: [Errno None] b'libusb0-dll:err [control_msg] sending control message failed, win error: A device which does not exist was specified.\r\n\n'
Does anyone know what i need to do to make this work.
I have installed libusb into my System32 and SysWOW64 folders, aswell as installing a libusb-32 driver for my printer with zadig.
The printer i'm using is a 'Hoin 58mm POS Printer'.
I would be grateful if someone could explain to me why i'm having this error and how to solve it!

Firstly, you can check this link for the complete thread.
As suggested by KM4YRI,
I ran into the same No backend available exception when trying to follow the tutorial on a Windows 7 machine. The following worked for me, per one of the StackOverflow replies:
1. Download the latest Windows binary: https://sourceforge.net/projects/libusb/files/libusb-1.0/libusb-1.0.21/libusb-1.0.21.7z/download
2. Unzip using 7zip into a temp dir
3. If on 64-bit Windows, copy `MS64\dll\libusb-1.0.dll` into `C:\windows\system32`. If on 32-bit windows, copy `MS32\dll\libusb-1.0.dll` into `C:\windows\SysWOW64`.
I've verified the above answer on Windows-10 64-bit version.

I had a tight experience with that error using at least 3 different USB Storage Devices. After hours of trials I ended up to a feeling that USB transmission errors are the cause of this error.
The USB bus will return it in a random pattern for a low quality connection as if a device remove has presumably happened.
In my scenario I was bulk writing sectors to a \\.\PhysicalDriveN device and I noticed that after a short period the connection reestablished and the file handle was still valid and going.
To overcome the error I've ended up with the following steps:
Seek To File Position;
Write Sector;
For any 433 error:
250 ms delay;
Seek To file Position, ignoring ERROR_NO_SUCH_DEVICE and ERROR_NOT_READY errors and trying for at least 1000 ms before giving up;
Read Sector, ignoring ERROR_NO_SUCH_DEVICE and ERROR_NOT_READY errors and retrying for up to 1000 ms before giving up;
Specially for my scenario: I've compared input buffer and read buffer and stop if matching;
Repeat the whole procedure up to 5 times.
So the idea here is the following: The device driver returns ERROR_NO_SUCH_DEVICE assuming a device remove scenario, but still in a pending state. As the problem is simply quality of physical connection, the link continues and the bus driver starts a renegotiation, in which case a ERROR_NOT_READY is temporarily returned. When the link is stable and negotiated, communication continues without the need to reopen the device handle.

I would recommend adding a sleep statement of a second or two in between the instantiation of the USB printer, and the attempt to print to it. e.g:
from escpos.printer import Usb
from time import sleep
p = Usb(0x0456,0x0808)
sleep(1)
p.text('Hello World\n')

Official Softlayer script to retrieve locations ids does not work

I used to use the following script for retrieving the different locations ids, to create an VSI order:
https://softlayer.github.io/python/list_packages/
Specifically:
def getAllLocations(self):
mask = "mask[id,locations[id,name]]"
result = self.client['SoftLayer_Location_Group_Pricing'].getAllObjects(mask=mask);
pp(result)
Unfortunately meanwhile it throws the following exception:
Traceback (most recent call last):
File "new.py", line 59, in <module>
main.getAllLocations()
File "new.py", line 52, in getAllLocations
result = self.client['SoftLayer_Location_Group_Pricing'].getAllObjects(mask=mask);
File "/usr/local/lib/python2.7/site-packages/SoftLayer/API.py", line 392, in call_handler
return self(name, *args, **kwargs)
File "/usr/local/lib/python2.7/site-packages/SoftLayer/API.py", line 360, in call
return self.client.call(self.name, name, *args, **kwargs)
File "/usr/local/lib/python2.7/site-packages/SoftLayer/API.py", line 263, in call
return self.transport(request)
File "/usr/local/lib/python2.7/site-packages/SoftLayer/transports.py", line 195, in __call__
raise _ex(ex.faultCode, ex.faultString)
SoftLayer.exceptions.SoftLayerAPIError: SoftLayerAPIError(SOAP-ENV:Server): Internal Error
Is there something that needs to be changed within the function?

Nope your code is fine the problem is that this is an issue with the method which is not working I am gonna report the issue or if you want it you can open an softlayer's ticket and report the issue yourself.

An issue with the getAllObjects method was fixed yesterday for this service. Please try the request again.

Tweepy issues with twitter bot and python

I have a few twitterbots that I run on my raspberryPi. I have most functions wrapped in a try / except to ensure that if something errors it doesn't break the program and continues to execute.
I'm also using Python's Streaming library as my source of monitoring for the tags that I want the bot to retweet.
Here is an issue that happens that kills the program although I have the main function wrapped in a try/except:
Unhandled exception in thread started by <function startBot5 at 0x762fbed0>
Traceback (most recent call last):
File "TwitButter.py", line 151, in startBot5
'<botnamehere>'
File "/home/pi/twitter/bots/TwitBot.py", line 49, in __init__
self.startFiltering(trackList)
File "/home/pi/twitter/bots/TwitBot.py", line 54, in startFiltering
self.myStream.filter(track=tList)
File "/usr/local/lib/python3.4/dist-packages/tweepy/streaming.py", line 445, in filter
self._start(async)
File "/usr/local/lib/python3.4/dist-packages/tweepy/streaming.py", line 361, in _start
self._run()
File "/usr/local/lib/python3.4/dist-packages/tweepy/streaming.py", line 294, in _run
raise exception
File "/usr/local/lib/python3.4/dist-packages/tweepy/streaming.py", line 263, in _run
self._read_loop(resp)
File "/usr/local/lib/python3.4/dist-packages/tweepy/streaming.py", line 313, in _read_loop
line = buf.read_line().strip()
AttributeError: 'NoneType' object has no attribute 'strip'
My setup:
I have a parent class TwitButter.py, that creates an object from the TwitBot.py. These objects are the bots, and they are started on their own thread so they can run independently.
I have a function in the TwitBot that runs the startFiltering() function. It is wrapped in a try/except, but my except code is never triggered.
My guess is that the error is occurring within the Streaming library. Maybe that library is poorly coded and breaks on the line that is specified at the bottom of the traceback.
Any help would be awesome, and I wonder if others have experienced this issue?
I can provide extra details if needed.
Thanks!!!

This actually is problem in tweepy that was fixed by github #870 in 2017-04. So, should be resolved by updating your local copy to latest master.
What I did to discover that:
Did a web search to find the tweepy source repo.
Looked at streaming.py for context on the last traceback lines.
Noticed the most recent change to the file was the same problem.
I'll also note that most of the time you get a traceback from deep inside a Python library, the problem comes from the code calling it incorrectly, rather than a bug in the library. But not always. :)

pydev multithread debugging

I'm trying to debug an application which makes use of the pynetdicom library. I'm not sure how relevant that specific detail is, however what IS relevant is that it makes heavy use of multithreading to run background socket listener tasks without blocking the main thread. The storescp.py example can be used to reproduce this.
Whenever I place a breakpoint that gets encountered (regardless of what thread, main or child, it gets encountered in), I get the following traceback:
Traceback (most recent call last):
File "/Applications/Aptana Studio 3/plugins/org.python.pydev_2.7.0.2013012902/pysrc/pydevd.py", line 1397, in <module>
debugger.run(setup['file'], None, None)
File "/Applications/Aptana Studio 3/plugins/org.python.pydev_2.7.0.2013012902/pysrc/pydevd.py", line 1090, in run
pydev_imports.execfile(file, globals, locals) #execute the script
File "/Users/alexw/Development/Python/kreport2/KReport2/dicomdatascraper.py", line 183, in <module>
oldDicomList = copy.copy(newData)
File "/Users/alexw/Development/Python/kreport2/KReport2/dicomdatascraper.py", line 183, in <module>
oldDicomList = copy.copy(newData)
File "/Applications/Aptana Studio 3/plugins/org.python.pydev_2.7.0.2013012902/pysrc/pydevd_frame.py", line 135, in trace_dispatch
self.doWaitSuspend(thread, frame, event, arg)
File "/Applications/Aptana Studio 3/plugins/org.python.pydev_2.7.0.2013012902/pysrc/pydevd_frame.py", line 25, in doWaitSuspend
self._args[0].doWaitSuspend(*args, **kwargs)
File "/Applications/Aptana Studio 3/plugins/org.python.pydev_2.7.0.2013012902/pysrc/pydevd.py", line 832, in doWaitSuspend
self.processInternalCommands()
File "/Applications/Aptana Studio 3/plugins/org.python.pydev_2.7.0.2013012902/pysrc/pydevd.py", line 360, in processInternalCommands
thread_id = GetThreadId(t)
File "/Applications/Aptana Studio 3/plugins/org.python.pydev_2.7.0.2013012902/pysrc/pydevd_constants.py", line 140, in GetThreadId
return thread.__pydevd_id__
File "/Users/alexw/.virtualenvs/kreport2dev/devlibs/pynetdicom/source/netdicom/applicationentity.py", line 73, in __getattr__
obj = eval(attr)()
File "<string>", line 1, in <module>
NameError: name '__pydevd_id__' is not defined
My thought is that, perhaps, in order to make things work, PyDev monkey-patches a __pydevd_id__ into spawned threads, however fails to patch those into these threads because they are, in fact, subclasses and not direct instances of threading.Thread (in this case, the worker is an instance of class Association(threading.Thread):).
Of course, I don't know PyDev well enough to confirm this theory, or else fix it. And it seems neither does the internet.
Is subclassing Thread so rarely used a pattern that it's simply not considered in the PyDev architecture? Without re-architecting the library, how could this issue be remedied?

I simply needed to look harder at that traceback.
The pynetdicom library, in its subclassing of threading.Thread, overrode __getattr__ and somewhat broke it. The problem was:
def __getattr__(self, attr):
#while not self.AssociationEstablished:
# time.sleep(0.001)
obj = eval(attr)
# do some stuff
return obj
when a nonexistent attribute is passed, a NameError is raised. This isn't caught by pydev's monkeypatching routine (if thread.__pydevd_id__ raises AttributeError, thread.__pydevd_id__ = stuff)
The solution was to update that section thusly:
def __getattr__(self, attr):
#while not self.AssociationEstablished:
# time.sleep(0.001)
try:
obj = eval(attr)
except NameError:
raise AttributeError
# do some stuff
return obj
This intercepts the NameError and raises an AttributeError instead, as __getattr__ should if the queried attribute doesn't exist.