# (Python) Source Block Outputs All 0's **URL:** \ **Category:** GNU Radio\ **Created:** [February 18, 2014, 7:51pm UTC](https://www.ruby-forum.com/t/python-source-block-outputs-all-0s/239247 "2014-02-18T19:51:35Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\ **Post date:** [February 18, 2014, 7:51pm UTC](https://www.ruby-forum.com/t/python-source-block-outputs-all-0s/239247/1 "2014-02-18T19:51:35Z")
Hi All, I have implemented a python source block: ``` def __init__ (self, kA1=4,kB1=4,k2=4,NA1=8,NB1=8,N2=8,M=8): gr.sync_block. __init__ (self, name="blsd_enc_b", in_sig=None, out_sig=[numpy.uint8,numpy.uint8]) ``` but I can’t get it to output anything but 0’s… ``` def work(self, input_items, output_items): out_cA = output_items[0] out_cB = output_items[1] out_cA = [5, 6, 7, 8, 9, 10] #cA[0] out_cB = [5, 6, 7, 8, 9, 10] #cB[0] self.produce(0,len(out_cA)) self.produce(1,len(out_cB)) print 'out_cA = ', out_cA, ', len(out_cA) = ', len(out_cA) print 'out_cB = ', out_cB, ', len(out_cB) = ', len(out_cB) return -1 #-2 ``` I connect both outputs to a file sync of type byte, and it stores 6 bytes but its all “\00\00\00\00\00\00” The print lines give: out\_cA = [5, 6, 7, 8, 9, 10] , len(out\_cA) = 6 out\_cB = [5, 6, 7, 8, 9, 10] , len(out\_cB) = 6 as expected. Any advice? Regards, David * * * NOTE: The information in this email and any attachments may be confidential and/or legally privileged. This message may be read, copied and used only by the intended recipient. If you are not the intended recipient, please destroy this message, delete any copies held on your system and notify the sender immediately. Toshiba Research Europe Limited, registered in England and Wales (2519556). Registered Office 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, England. Web: www.toshiba.eu/research/trl ---
**Author:** ![divotdave](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/bbe5ce/32.png) [@divotdave](https://www.ruby-forum.com/u/divotdave)\ **Post date:** [February 18, 2014, 10:07pm UTC](https://www.ruby-forum.com/t/python-source-block-outputs-all-0s/239247/2 "2014-02-18T22:07:36Z")
On Tue, Feb 18, 2014 at 12:50 PM, David Halls [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > print 'out\_cA = ', out\_cA, ', len(out\_cA) = ', len(out\_cA) > out\_cB = [5, 6, 7, 8, 9, 10] , len(out\_cB) = 6 > > as expected. > > Any advice? > > Regards, > > David David, The problem here is that you’re not inserting items in to the out\_cA (and out\_cB) arrays, you’re actually reassigning out\_cA to be this new list. Honestly, I’ve never written a python block, but my understanding is that you’d have to do something like this [http://dpaste.com/1634971/](http://dpaste.com/1634971/) The items in the out\_items list are actually numpy arrays, and they need to be indexed. The [:] indexing is a shortcut of indexing the entire array. Another thing I’m not really sure about is whether the -1 will work or not. I think you might have to return 6 so that the scheduler knows there are 6 items to work on, and then the next time work is called you return -1 ( assuming you’re wanting to stop the flowgraph here?). Somebody else might chime in here if I’m wrong. Nathan ---
**Author:** ![divotdave](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/bbe5ce/32.png) [@divotdave](https://www.ruby-forum.com/u/divotdave)\ **Post date:** [February 18, 2014, 11:13pm UTC](https://www.ruby-forum.com/t/python-source-block-outputs-all-0s/239247/3 "2014-02-18T23:13:00Z")
Hi Nathan, Thanks for your reply 🙂 I’ve done little python before, am trying to incorporate a collaborators code into my system and he’s used python. I am used to C, where it would copy the pointer. I understand your advice - thanks, I will look at the link. The return value is mimicking the WORK\_CALLED\_PRODUCE (-2) and WORK\_DONE return values that can be used when you have multiple outputs which may output different number of items and the produce function is used. I am not sure why the block keeps repeating if I use -2 as I use successfully in many c++ blocks - I’m not used to writing source blocks… maybe others have comments? David * * * From: West, Nathan [removed\_email\_address@domain.invalid] Sent: 18 February 2014 21:06 To: David Halls Cc: GNURadio D.ion List Subject: Re: [Discuss-gnuradio] (Python) Source Block Outputs All 0’s On Tue, Feb 18, 2014 at 12:50 PM, David Halls [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > print 'out\_cA = ', out\_cA, ', len(out\_cA) = ', len(out\_cA) > out\_cB = [5, 6, 7, 8, 9, 10] , len(out\_cB) = 6 > > as expected. > > Any advice? > > Regards, > > David David, The problem here is that you’re not inserting items in to the out\_cA (and out\_cB) arrays, you’re actually reassigning out\_cA to be this new list. Honestly, I’ve never written a python block, but my understanding is that you’d have to do something like this [http://dpaste.com/1634971/](http://dpaste.com/1634971/) The items in the out\_items list are actually numpy arrays, and they need to be indexed. The [:] indexing is a shortcut of indexing the entire array. Another thing I’m not really sure about is whether the -1 will work or not. I think you might have to return 6 so that the scheduler knows there are 6 items to work on, and then the next time work is called you return -1 ( assuming you’re wanting to stop the flowgraph here?). Somebody else might chime in here if I’m wrong. Nathan * * * NOTE: The information in this email and any attachments may be confidential and/or legally privileged. This message may be read, copied and used only by the intended recipient. If you are not the intended recipient, please destroy this message, delete any copies held on your system and notify the sender immediately. Toshiba Research Europe Limited, registered in England and Wales (2519556). Registered Office 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ, England. Web: www.toshiba.eu/research/trl