So, I got this wired thing when using list with bytes inside on a Raspberry Pi Pico and MicroPython.
If I use binascii.hexlify(data_raw[0]).decode() I got the error TypeError: object with buffer protocol required
The list is like below:
[b'\x02', b'\x88', b'\x84', b'\x80', b'\x80']
Instead, if I use binascii.hexlify(b'\x02').decode() everything works fine
I can't understand the issue
Related
I managed to install and successfully import cv2 on a linux(Debian) virtual machine, using python 2.7. I tried to take a picture using my webcam with the following piece of code:
import cv2
from datetime import datetime
tar_file = datetime.now().strftime("%Y%m%d-%H%M%S") + '.png'
camera_port = 0
ramp_frames = 30
camera = cv2.VideoCapture(camera_port)
def get_image():
retval, im = camera.read()
return im
for i in xrange(ramp_frames):
temp = get_image()
camera_capture = get_image()
cv2.imwrite(tar_file, camera_capture)
camera = None
I have tested the code earlier on my windows 10 host machine and it works fine. When using this code the program successfully saves the file, but the file cannot be opened and the following error is displayed in the terminal:
libpng warning: Image width is zero in IHDR
libpng warning: Image height is zero in IHDR
libpng error: Invalid IHDR data
The error occurs as the camera_capture object is a NoneType, why is this so?
How can I prevent this error from happening and successfully take a snapshot through my webcam?
Edit : The error appears the occur when the line "cv2.imwrite(tar_file, camera_capture)" is run. Upon further inspection the camera_capture variable is a NoneType and the retval value is False which would explain the width and height being 0. Why is the variable a NoneType and how can I prevent this from happening?
The code is failing due to no data being written to the file. This causes the file to be empty and thus it cannot be opened. The reason the data returned is empty is most likely due to an incorrectly configured webcam. The solution to this is to connect the VM to the camera. If it still fails, try to install a driver on the VM for the webcam.
The Point Cloud library comes with an executable pcl_hdl_viewer_simple that I can run (./pcl_hdl_viewer_simple) without any extra arguments to get live data from a Velodyne LIDAR HDL32.
The source code for this program is supposed to be hdl_viewer_simple.cpp. A simplified version of the code is given on this page which cannot be compiled readily and requires a tiny bit of tweaking to make it compile.
My problem is that the executable that I build myself for both the versions are not able to run. I always get the smart pointer error "Assertion px!=0" error. I am not sure if I am not executing the program in the correct way or what. The executable is supposed to be executed like
./hdl_viewer_simple -calibrationFile hdl32calib.xml -pcapFile file.pcap
in case of playing from previously recorded PCAP files or just ./hdl_viewer_simple if wanting to get live data from the real sensor. However, I always get the assertion failed error.
Has anyone been able to run the executables? I do not want to use the ROS drivers
"Assertion px!=0" is occurring because your pointer is not initialized.
Now that being said, you could initialize it inside your routines, in case the pointer is NULL, especially for data input.
in here, you can try updating the line 83 like this :
CloudConstPtr cloud(new Cloud); //initializing your pointer
and hopefully, it will work.
Cheers,
I'm new to scapy.
I'm trying to combine scapy in a script, and not use it through bash.
I'm intending to forge a packet.
By all the tutorials and .pdf's I saw, all explaining how to do it inside the scapy tool(in bash).
I tried the following code:
from scapy.all import *
a=IP()
a.src="10.0.0.30"
a.dst="10.0.0.138"
print a
I tried this just to get a print output like I would get in bash, that will look like:
<IP src=10.0.0.20 dst=10.0.0.138|>
but insted I get unknown symbols, something like:
"EXX#f#
?"
My question is how do I get the same output that I got in bash??? I mean viewing the fields that I inserted.
Thanks for the responders.
The print statement in Python when used on a Scapy object will output the raw bytes of a packet.
You should use the .show() function for the packet you created to get the nice output you are expecting. Try the following in your python program.
a.show()
a.show2()
See this Send and Receive example in the Scapy docs for more.
A list of for examining the contents of the packet is also found here - just scroll down to the "Command/Effect" table.
I'm trying to use libPd, the wrapper for PureData.
But the documentation is poor and I'm not very into C++
Do you know how I can simply send a floating value to a Pd patch?
Do I need to install libPd or I can just include the files?
First of all, check out ofxpd. It has an excellent libpd implementaiton with OpenFrameworks. If you are starting with C++ you may want to start with OpenFrameworks since it has some great documentation and nice integration with Pd via the ofxpd extension.
There are two good references for getting started with libpd (though neither cover C++ in too much detail): the original article and Peter Brinkmann's book.
On the libpd wiki there is a page for getting started with libpd. The linked project at the bottom has some code snippets in main.cpp that demonstrate how to send floats to your Pd patch.
pd.sendBang("fromCPP");
pd.sendFloat("fromCPP", 100);
pd.sendSymbol("fromCPP", "test string");
In your Pd patch you'll set up a [receive fromCPP] and then these messages will register in your patch.
In order to get the print output you have to use the receivers from libpd in order to receiver the strings and then do something with them. libpd comes with PdBase, which is a great class for getting libpd up and running. PdBase has sendBang, sendFloat, sendMessage, and also has the receivers set up so that you can get output from your Pd patch.
if you want to send a value to a running instance of Pd (the standalone application), you could do so via Pd's networking facilities.
e.g.
[netreceive 65432 1]
|
[route value]
|
[print]
will receive data sent from the cmdline via:
echo "value 1.234567;" | pdsend 65432 localhost udp
you can also send multiple values at once, e.g.
echo "value 1.234567 3.141592;" | pdsend 65432 localhost udp
if you find pdsend to slow for your purposes (e.g. if you launch the executable for each message you want to send you have a considerable overhead!), you could construct the message directly in your application and use an ordinary UDP-socket to send FUDI-messages to Pd.
FUDI-messages really are simple text strings, with atoms separated by whitespace and a terminating semicolon, e.g.
accelerator 1.23 3.14 2.97; button 1;
you might also considering using OSC, but for this you will need some externals (OSC by mrpeach; net by mrpeach (or iemnet)) on the Pd side.
as for performance, i've been using the latter with complex tracking data (hundreds of values per frame at 125fps) and for streaming multichannel audio, so i don't think this is a problem.
if you are already using libPd and only want to communicate from the host-application, use Adam's solution (but your question is a bit vague about that, so i'm including this answer just in case)
I've got a fairly simple USB HID device that I've been trying to figure out how to read from and write to using Python. I've been able to read from it using PyWinUSB, but the problem comes in when I try to write to it. Trying to write to it makes things explode.
For example:
device = hid.HidDeviceFilter(vendor_id = 0x0003, product_id = 0x1001).get_devices()[0]
This works fine. Then for reading raw data, which is all that I care about right now (I'll work with that once I can figure out how to write to the cursed thing):
def readData(data):
print(data)
return None
This works fine (in fact, it was quite exciting when I got to see it work). So I would assign the data handler like so:
device.set_raw_data_handler(readData)
And every time I hit a button, it's fine. The data comes through as you would expect. Which is great!
The problem comes when I want to write to the device.
Following the sample simple_send file as a template (which was probably not the best choice), I would do the following:
report = device.find_output_reports()[0]
Which would return a report object with a dictionary holding 4 entries. Is that correct? Do you write to a device using the output_reports object? Trying to do so by setting the report value to ANYTHING:
report[<key>] = "pneumonoultramicroscopicvolcanoconiosis"
report.send()
This would keep returning some obnoxious error that I can't interpret:
Traceback (most recent call last):
File "<pyshell#21>", line 1, in <module>
report.send()
File "C:\Python27\lib\site-packages\pywinusb-0.3.1-py2.7.egg\pywinusb\hid\core.py", line 1446, in send
self.__prepare_raw_data()
File "C:\Python27\lib\site-packages\pywinusb-0.3.1-py2.7.egg\pywinusb\hid\core.py", line 1401, in __prepare_raw_data
byref(self.__raw_data), self.__raw_report_size) )
File "C:\Python27\lib\site-packages\pywinusb-0.3.1-py2.7.egg\pywinusb\hid\winapi.py", line 382, in __init__
raise helpers.HIDError("hidP error: %s" % self.error_message_dict[error_code])
HIDError: hidP error: data index not found
I'm using Windows 7. I've managed to find (finally) a reference for the HID DLL exported functions, and I don't HAVE to (or, for that matter even really WANT to) use the PyWinUSB library. I just want to make this work, and it didn't seem like it would be that tough, but it has been.
Can someone tell me what it is I've been doing wrong here?
Thanks.
Also, I tried tracing the error call, and made it so far before the program just closed which was kind of disheartening.
i made it work with this
buffer= [0xFF]*33 # 33 = report size + 1 byte (report id)
buffer[0]=0x0 # report id
buffer[1]=0xFE
buffer[2]=0x00
buffer[3]=0xFF
out_report.set_raw_data(buffer)
out_report.send()
dev.close()
For me worked only this:
report.send([0x70, ..., 0x73 ])
The function call sequence with set_raw_data([0x70, ..., 0x73) and subsequent send() didn't work for me.