python 3 support, ctypes error?

[tobeycarman]

I am trying to build aravis and python-aravis in a python3 environment and I am getting a ctypes.cast error.

I am on Ubuntu 16.04, and I installed python3.6 under conda. I was able to build aravis, and python-aravis with no errors (although I did have to monkey-patch aravis.py to import pgi instead of import gi). I then run my test script which is this:

#!/usr/bin/env python

import pgi
pgi.require_version('Aravis', '0.6')

import aravis
import time
import sys

FRAMES=4

available_cameras = aravis.get_device_ids()
if len(available_cameras) > 0:
  cam = aravis.Camera(available_cameras[0])
else:
  print("No camera is on. Quitting.")
  sys.exit(-1)  

cam.start_acquisition()
for i in range(0, FRAMES):
  print("Sleeping while capturing images...")
  time.sleep(1)
print("Stopping acq...")
cam.stop_acquisition()

print("Gonna show you some images here...")
for i in range(0, 2):
  print("Popping a frame...")
  try:
    d = cam.pop_frame()
    print("Frame {} is:".format(i))
    print(d)
  except Exception as e:
    print("UH OH, there was a problem!: ", e)
    raise e

for i in range(0, FRAMES):
  try:
    print("Saving {} of 5 frames...".format(i))
    aravis.sfn(cam, app.config['IMAGES_INCOMING'])
  except Exception as e:
    print("UH OH, there was a problem!: ", e)
    raise e

When I run my test script I get this:

$ ./test.py 
Sleeping while capturing images...
Sleeping while capturing images...
Sleeping while capturing images...
Sleeping while capturing images...
Stopping acq...
Gonna show you some images here...
Popping a frame...
UH OH, there was a problem!:  argument 1: <class 'TypeError'>: wrong type
Traceback (most recent call last):
  File "./test.py", line 35, in <module>
    raise e
  File "./test.py", line 30, in <module>
    d = cam.pop_frame()
  File "/home/vagrant/anaconda3/envs/py3/lib/python3.6/site-packages/aravis-0.5-py3.6.egg/aravis.py", line 153, in pop_frame
  File "/home/vagrant/anaconda3/envs/py3/lib/python3.6/site-packages/aravis-0.5-py3.6.egg/aravis.py", line 169, in try_pop_frame
  File "/home/vagrant/anaconda3/envs/py3/lib/python3.6/site-packages/aravis-0.5-py3.6.egg/aravis.py", line 191, in _array_from_buffer_address
  File "/home/vagrant/anaconda3/envs/py3/lib/python3.6/ctypes/__init__.py", line 485, in cast
    return _cast(obj, obj, typ)
ctypes.ArgumentError: argument 1: <class 'TypeError'>: wrong type

[tobeycarman]

Partially figured this out - pip installed package pgi does not seem to work, but if I install the gi package using apt-get, it works (sudo apt-get install python-gi)

So this dosen't really have to do with python3 at all. I suspect it is some small different in implementation between the python-gi implementation of introspection vs the pgi implementation of introspection.

[IamSierraCharlie]

For python 3, I thought you needed pip3 rather than pip
on ubuntu
sudo apt-get install python3-pip
then do
pip3 install pgi

The above works for me on Ubuntu
##############################
pip3 install pgi
Collecting pgi
Downloading pgi-0.0.11.1.tar.gz (235kB)
100% |¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦| 245kB 2.4MB/s
Building wheels for collected packages: pgi
Running setup.py bdist_wheel for pgi ... done
Stored in directory: /home/s/.cache/pip/wheels/cc/9e/e2/a9c5dda8bc0bd98379827b52a97c0f593034d1094a55f689e7
Successfully built pgi
Installing collected packages: pgi
Successfully installed pgi-0.0.11.1
####################################
Distributor ID: Ubuntu
Description: Ubuntu 16.04.2 LTS
Release: 16.04
Codename: xenial

I'm no expert in python, but in my own experience I've found using pip / pip3 to be a better way to manage python packages over using apt.
Someone with more experience may suggest otherwise.
Steve

[tobeycarman]

@IamSierraCharlie, I agree re: pip vs apt-get. I always start with pip, but occasionally there is something I can't find with pip that is available with apt-get.

In my first post, I was actually trying to use the conda package manager (https://www.continuum.io/downloads) but I got really confused.

I now have it working, and like I said, I think the problem before was that the pgi that I installed with pip was giving that error out of ctypes.cast(...), where as if I install gi (which I can't find in pip, but I did find with apt-get), then everything works perfectly...

At this point I've reduced myself to only needing python-virtualenv, python-gi, and python-dev from the apt-get repos, and everything else I can get with pip.