Experimental Physics and
Industrial Control System

Hi Liang-Chih, 

On Wed, Jan 8, 2020 at 9:29 PM Chiang, Liang-Chih [江良志] via Tech-talk <[email protected]> wrote:

Hi,

I could install PyEpics on CentOS 6.10(x86_64) and Python 3.7,

and there is no problem using caget, caput, PV, Motor, etc.. of PyEpics.

However, in the following environment, 'import epics' will result in error.

    CentOS version 7.4, x86_64 architecture

    Linux kernel version 3.10.0

    Python 3.7 (created by Miniconda virtual environment)

The PyEpics was installed by the following command:

$ conda install -c GSECARS pyepics

In Python interactive shell:

>>> import epics

Traceback (most recent call last):

  File "/home/user/miniconda3/envs/py37/lib/python3.7/ctypes/__init__.py", line 97, in CFUNCTYPE

    return _c_functype_cache[(restype, argtypes, flags)]

KeyError: (None, (<class 'epics.dbr.access_rights_handler_args'>,), 1)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

  File "/home/user/miniconda3/envs/py37/lib/python3.7/site-packages/epics/__init__.py", line 29, in <module>

    from . import ca

  File "/home/user/miniconda3/envs/py37/lib/python3.7/site-packages/epics/ca.py", line 761, in <module>

    dbr.access_rights_handler_args)

  File "/home/user/miniconda3/envs/py37/lib/python3.7/site-packages/epics/dbr.py", line 339, in make_callback

    return ctypes.CFUNCTYPE(None, args)(func)

  File "/home/user/miniconda3/envs/py37/lib/python3.7/ctypes/__init__.py", line 99, in CFUNCTYPE

    class CFunctionType(_CFuncPtr):

TypeError: item 1 in _argtypes_ passes a struct/union with a bitfield by value, which is unsupported.

I also tried installing PyEpics by 'pip install pyepics', similar error message will show up when installing.

Best regards.

 

LiangChih Chiang

email: [email protected]

Beamline Group

National Synchrotron Radiation Research Center (NSRRC)

Sorry for the trouble.    As it turns out, this was raised as an Issue earlier today (see https://github.com/pyepics/pyepics/issues/189).  

The problem is not actually related to CentOS version.   

We've verified that the problem happens with Python 3.7.6, but not with Python 3.7.5.  It also appears that pyepics works with Python 3.8.0.  I don't think anyone has tested it with Python 3.8.1, I suspect that may fail too as it was released at the same time as 3.7.6.   As it happens, it looks like updating an Anaconda Python 3.7 environment will now upgrade to Python 3.7.6. 

We're still tracking down the problem: it looks like our wrapping of the CA `access_rights_handler_args` structure fails with the latest version.  We don't have a proposed solution yet, but some ideas.

I hope we can get this fixed soon.  In the meantime, I think rolling back to Python 3.7.5 is probably the simplest solution.

--Matt Newville