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Re: [Discuss-gnuradio] Python pass parameter as const *gr_complex?

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Python pass parameter as const *gr_complex?
Date: Wed, 21 Jan 2015 08:50:04 -0500

On Wed, Jan 21, 2015 at 3:13 AM, Ludwig Stephan (CR/AEH4) <address@hidden> wrote:
Thank you, Tom, for your enlightening answer. Please let me ask two additional questions:

1) If I understood your explanation correctly, as a consequence of this, one could not use the decision_maker method within a block, which is coded solely in python. Right?

2) Isn't "const gr_complex*" a type, which is used very often in the block I/O interfaces, and shouldn't, thus, the GR configuration of SWIG already let it know how to translate python/complex to gr_complex?

No. That type is almost never used. What is often used is "const std::vector<gr_complex>". But again, this class was designed to be called from within a block's work function, so the data structure would have already been a "const gr_complex*" (casting the input_items argument).



Best regards

Stephan Ludwig

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Von: address@hidden [mailto:address@hidden] Im Auftrag von Tom Rondeau
Gesendet: Dienstag, 20. Januar 2015 15:57
An: Ludwig Stephan (CR/AEH4)
Cc: address@hidden
Betreff: Re: [Discuss-gnuradio] Python pass parameter as const *gr_complex?

On Wed, Jan 7, 2015 at 7:57 AM, Ludwig Stephan (CR/AEH4) <address@hidden> wrote:
Hi list,
I am trying to use the gr::digital::constellation::decision_maker(.) method from python, but I get an error message.
In order to reproduce call in python:
import gnuradio.digital
a = gnuradio.digital.constellation_qpsk()
b = complex(1+1j)
=> TypeError [..] argument 2 of type ‘gr_complex const*’
The C++-implementation is wrapped by SWIG, where the error occurs.
This might be a silly question, but what am I doing wrong?
Thanks for any help.
Best regards
Stephan Ludwig

Hi Stephan,

You're not doing anything wrong per se, but the block isn't really meant to be used that way. SWIG needs to be told how to handle some types of argument formats, and it hasn't been told how to handle this one.

The post 3.7 way we've been handling SWIG is to just include the public .h file as the interface, so all methods are exported into SWIG. A class like this needs that method to be public for use as a contained object in the block that calls it, but it's not really meant for use outside like this. Not that it couldn't be, but you'd have to work with SWIG to let it understand how to call that function with the proper input type.


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