AttributeError: 'QuantumCircuit' object has no attribute 'config'

Question

I am working on a program for Qiskit, but I am getting a strange error (one that I have not gotten in the past) when I try to simulate a circuit. Here is a minimal example producing the error:

from qiskit.circuit import QuantumCircuit
from qiskit import Aer,transpile

c = QuantumCircuit(2)
simulator = Aer.get_backend('qasm_simulator')
c = transpile(c, simulator)
result = simulator.run(c).result()
plot_histogram(counts, title='Counts')

The error I get is:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-1-89904ecd5f8e> in <module>()
      5 simulator = Aer.get_backend('qasm_simulator')
      6 c = transpile(c, simulator)
----> 7 result = simulator.run(c).result()
      8 plot_histogram(counts, title='Counts')

/Users/d/anaconda3/envs/qiskit/lib/python3.7/site-packages/qiskit/providers/aer/backends/aerbackend.py in run(self, qobj, backend_options, validate, **run_options)
    146         # Add backend options to the Job qobj
    147         qobj = self._format_qobj(
--> 148             qobj, backend_options=backend_options, **run_options)
    149 
    150         # Optional validation

/Users/d/anaconda3/envs/qiskit/lib/python3.7/site-packages/qiskit/providers/aer/backends/aerbackend.py in _format_qobj(self, qobj, backend_options, **run_options)
    353         """Return execution sim config dict from backend options."""
    354         # Add options to qobj config overriding any existing fields
--> 355         config = qobj.config
    356 
    357         # Add options

AttributeError: 'QuantumCircuit' object has no attribute 'config'

Does anyone know what is causing this error?

Thank you!

Answer 1

I believe you need to assemble the transpiled circuit in a qobj before running it :

from qiskit.compiler import assemble
my_qobj = assemble(c)
result = simulator.run(my_qobj).result()

By the way, without any measure, the plot_histogram(result.get_counts()) will return an error as well.

There is also a special platform the Quantum Computing, https://quantumcomputing.stackexchange.com, feel free to post any other questions about QC&co there :)