RuntimeError: Too Many Compiler Engines Added to the MainEngine in ProjectQ

[saifawan2703]

Hi everyone,

I’m encountering an issue when trying to run a quantum circuit using ProjectQ. Specifically, I’m getting the following error:
RuntimeError: Too many compiler engines added to the MainEngine!
The error is raised from this part of the code:
File "/home/qc/anaconda3/lib/python3.12/site-packages/projectq/meta/_util.py", line 32, in insert_engine raise RuntimeError('Too many compiler engines added to the MainEngine!') . Any suggestion or guidance to resolve this error.

[damiansteiger]

Too many compiler engines. The compiler engines are given as a parameter (engine_list) when initialising the MainEngine. Further compiler engines are temporarily added when meta instructions are used. E.g.
with Control will insert a compiler engine to add the control qubits to the gates within the with Control context. Once the context is exited, this additional engine disappears.

By default there are 100 (n_engines_max) compiler engines allowed, see doc MainEngine. One can change this value but nesting of meta instructions typically never reaches 100 unless there is a bug in the user code.