[Discuss-gnuradio] Non-uniform behaviour of swigged objects (was: [USRP-users] uhd.tune_request always returns 0)

Well, the python semantics, at least as I understand them, dictate that "not objectname" is True if objectname is of NoneType, or if objectname is actually False, or evaluates to something that is False (i.e. 0).

A valid object "should be".

Checking it against the typical swigged GNU Radio objects:

$from gnuradio import blocks, uhd
$vs = blocks_vector_sink_b()
$f = uhd.tune_request(10)
$bool(vs)
True
$bool(f)
False

That's non-uniform behaviour, and it surprises me!

I'll have to meditate about this.

Best regards,
Marcus

On 22.05.2016 17:51, Marcus D. Leech via USRP-users wrote:

On 05/22/2016 11:46 AM, Marcus Müller via USRP-users wrote:

Hm, interesting. I shouldn't have thought so, but: something's strange, and for some reason, perfectly valid uhd.tune_request objects evaluate to False in this case.

So: since there's hardly any case that you can mis-construct a tune request (any frequency that is numerical should be fine, even negative numbers), I'd say: drop your "if not tx_center_freq" clause and just check whether the properties of the uhd.tune_result that tx.set_center_freq() return match your expectation.

Best regards,
Marcus

What are the boolean semantics of a structured data type like a tune_request_t ?  It's not immediately clear to me that there is a mapping
  in boolean for such structured data types.

On 22.05.2016 17:32, Elvis Angelaccio via USRP-users wrote:

Hi, can someone explain me why `uhd.tune_request` always returns 0 in  the following Python code?  I'm running this on Linux with a USRP1 attached via USB.  The USRP has two 900 MHz daughterboards and two antennas attached to  TX/RX ports.    Gnuradio version = 3.7.9.2  UHD version = 3.9.3    ### CODE Snippet ####    d = uhd.find_devices(uhd.device_addr(args.address_args))  if d:      print 'Available UHD devices: ' + str(d)    try:      uhd_type = d[0].get('type')  except IndexError:      print 'Fatal error. Did you connect the USRP to an USB port?'      sys.exit(1)    serial = d[0].get('serial')  tx = uhd.usrp_sink(      device_addr='serial=' + serial,      stream_args=uhd.stream_args(          'fc32',          channels=range(1)      )  )    tx_center_freq = uhd.tune_request(freq)    if not tx_center_freq:   # <===== Always happening.      print 'Could not set TX freq'      sys.exit(1)    tx.set_center_freq(tx_center_freq)  ...      Best regards,  Elvis    _______________________________________________  USRP-users mailing list  USRP-users@lists.ettus.com  http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com  

_______________________________________________  USRP-users mailing list  USRP-users@lists.ettus.com  http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com  

_______________________________________________  USRP-users mailing list  USRP-users@lists.ettus.com  http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com