I am trying to make my own version of packet_rx.grc. I copied the flowgraph and began modifying it. I found that at some point I started getting this error when I open the flowgraph:
ERROR:gnuradio.grc.core.FlowGraph:Failed to evaluate variable block modulated_sync_word
Traceback (most recent call last):
File "/home/user/git/toolbox/conda/miniforge3/envs/gnuradio/lib/python3.8/site-packages/gnuradio/grc/core/FlowGraph.py", line 268, in renew_namespace
value = eval(variable_block.value, namespace, variable_block.namespace)
File "<string>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'to_basic_block'
ERROR:gnuradio.grc.core.FlowGraph:Failed to evaluate variable block modulated_sync_word
Traceback (most recent call last):
File "/home/user/git/toolbox/conda/miniforge3/envs/gnuradio/lib/python3.8/site-packages/gnuradio/grc/core/FlowGraph.py", line 268, in renew_namespace
value = eval(variable_block.value, namespace, variable_block.namespace)
File "<string>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'to_basic_block'
I traced the problem back to whether or not the preamble variables are enabled in the flowgraph. However, it doesn't matter whether these variables are actually used anywhere. They simply need to exist otherwise this error occurs.
Please see the attached grc file. It has the minimum number of blocks to reproduce the error. If the 3 disabled blocks are instead enabled then the error will not occur.
modulate_vector_error_example.grc