# Hierarchical blocks (arbitrary or variable numbers of inputs or outputs not supported)

**URL:** <https://www.ruby-forum.com/t/hierarchical-blocks-arbitrary-or-variable-numbers-of-inputs-or-outputs-not-supported/231168>\
**Category:** GNU Radio\
**Created:** [July 24, 2014, 7:20pm UTC](https://www.ruby-forum.com/t/hierarchical-blocks-arbitrary-or-variable-numbers-of-inputs-or-outputs-not-supported/231168 "2014-07-24T19:20:51Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [July 24, 2014, 7:20pm UTC](https://www.ruby-forum.com/t/hierarchical-blocks-arbitrary-or-variable-numbers-of-inputs-or-outputs-not-supported/231168/1 "2014-07-24T19:20:51Z")

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Hello,

I am trying to create a hierarchical block with a variable number of  
outputs, but I get this error:  
“RuntimeError: Hierarchical blocks do not yet support arbitrary or  
variable numbers of inputs or outputs”

This appears to be a known issue [1], and I’m wondering what the best  
work around is. I think I can simply create an IO Signature with the  
maximum possible outputs I will need, and then connect a null source to  
all of the outputs I’m not intending to use. Is that a good idea?

Thanks,  
Orin

[1]  
[https://lists.gnu.org/archive/html/discuss-gnuradio/2009-04/msg00011.html](https://lists.gnu.org/archive/html/discuss-gnuradio/2009-04/msg00011.html)

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<div class="post-metadata">

**Author:** ![Orin\_L](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/90ced4/32.png) [@Orin\_L](https://www.ruby-forum.com/u/Orin_L)\
**Post date:** [July 24, 2014, 10:13pm UTC](https://www.ruby-forum.com/t/hierarchical-blocks-arbitrary-or-variable-numbers-of-inputs-or-outputs-not-supported/231168/2 "2014-07-24T22:13:46Z")

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On Thu, Jul 24, 2014 at 1:19 PM, Orin L. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> outputs I’m not intending to use. Is that a good idea?
> 
> Thanks,  
> Orin
> 
> [1] [discuss-gnuradio (date)](https://lists.gnu.org/archive/html/discuss-gnuradio/2009-04/)  
> msg00011.html

Orin,  
Yep, that’s the best way to handle this case.

Tom