Interrupted system call

[Peter Otten]

Chris Angelico wrote:

> On Mon, Nov 17, 2014 at 3:10 PM, Peter Bell <peter at bellfamily.org.uk>
> wrote:
>> Many thanks for your helpful response, Chris.
>>
>> On 17/11/14 06:13, Chris Angelico wrote:
>>>
>>> On Sun, Nov 16, 2014 at 7:11 PM, Peter Bell <peter at bellfamily.org.uk>
>>> wrote:
>>>>
>>>>    File "/usr/lib/python3.4/site-packages/serial/serialposix.py", line
>>>> 480,
>>>> in read
>>>>      if e[0] != errno.EAGAIN:
>>>> TypeError: 'InterruptedError' object is not subscriptable
>>>> =====================================================================
>>>>
>>>>
>>>> I'm not sure how to address the 'InterruptedError'.  Can it/should it
>>>> be
>>>> masked at the user code level with a 'try:' block?  Or is there another
>>>> way
>>>> to deal with it?
>>>
>>>
>>> At this stage, you're not getting it, because of the cascaded error,
>>> so that's the thing to deal with.
>>
>>
>> Okay - I was just thinking that if the 'InterruptedError' didn't occur,
>> then the 'TypeError' would never be exposed!
> 
> Correct. The handling of InterruptedError (a subclass of OSError) is
> what's raising TypeError.
> 
>> Ah, I understand. I believe, then, that this is from the pyserial module,
>> fetched from sourceforge.
>>
>> I see, now, that the sourceforge download does specify
>> 'pyserial-2.7.tar.gz'
>> and, yes, I'm working in Python 3.  I see, from other comments around the
>> web, that I'm not the only person to be attempting to use this module
>> with 3.
>>
>> Given that pyserial is for 2.7, it is probably unreasonable to report
>> errant behaviour when run on Python 3.
> 
> Yes and no. It may be possible to alter the code to be 2/3 compatible;
> for instance, if e.errno is used instead of e[0], it should work in
> both 2.7 and 3.x. (I haven't confirmed this, though.) But keep
> reading.
> 
>> I'm teaching myself (and the kids, as I go) Python and felt, rightly or
>> wrongly, that it would be better to start with Python 3, rather than
>> learning the older Python 2.x.
> 
> You felt rightly. All you need is...
> 
>> Is there a better way to interface to a serial port from Python 3?  I've
>> found a reference in the PSF 3.3.6 FAQ which points to pyserial on
>> sourceforge.
> 
> ... a solution to this. I would suggest looking on PyPI, the Python
> Package Index, to see what you can get for Python 3. In your case, you
> may well be in luck:
> 
> https://pypi.python.org/pypi/pyserial
> 
> There's a version that claims to work with any Python version (though
> there's some minor disagreement; the metadata says 2.3-2.7 and
> 3.0-3.3, but the Windows binaries say 2.4-2.7 and 3.0-3.4). I suspect
> the "2.7" in the name is actually the version of PySerial, and it's
> coincidental that that happens also to be a Python version.
> 
> Since you seem to be on a POSIX system, you shouldn't need to worry
> about the provided binary installers. Use pip3 to install it for your
> Python 3, and you should be all set.

I'd suggest a more conservative path: if available install the version that 
comes with your distribution. 

$ sudo apt-get python3-serial

might do the job.

> Now, since the package does claim to support Python 3, any
> discrepancies between that claim and the actual results you're seeing
> *are* reportable bugs. But it's entirely possible that using pip to
> install it will sort all that out, as it'll go and grab the correct
> version.
> 
> All the best!
> 
> ChrisA