I've been using qiskit for about a year now, and as of late, I've had issues finding an available backend to run my circuit on. Looking into the matter, I reinstalled qiskit to find that most everything had changed quite a bit. Now when I try to run just a basic test circuit program, taken from the tutorial I get this:

~$ python3 test.py

Traceback (most recent call last):
  File "test.py", line 27, in <module>
    job = execute(circ, backend)
  File "/home/micciche/.local/lib/python3.5/site-packages/qiskit/tools/compiler.py", line 108, in execute
    skip_transpiler, seed_mapper, pass_manager, memory)
  File "/home/micciche/.local/lib/python3.5/site-packages/qiskit/tools/compiler.py", line 67, in compile
    coupling_map=coupling_map, seed=seed, memory=memory)
  File "/home/micciche/.local/lib/python3.5/site-packages/qiskit/converters/circuits_to_qobj.py", line 61, in circuits_to_qobj
  File "/home/micciche/.local/lib/python3.5/site-packages/qiskit/converters/circuits_to_qobj.py", line 92, in _circuit_to_experiment
    json_circuit = DagUnroller(dag, JsonBackend(dag.basis)).execute()
  File "/home/micciche/.local/lib/python3.5/site-packages/qiskit/unroll/_dagunroller.py", line 38, in execute
  File "/home/micciche/.local/lib/python3.5/site-packages/qiskit/unroll/_dagunroller.py", line 161, in _process
    self.backend.new_qreg(name, width)
  File "/home/micciche/.local/lib/python3.5/site-packages/qiskit/unroll/_jsonbackend.py", line 98, in new_qreg
    assert size >= 0, "invalid qreg size"
  TypeError: unorderable types: QuantumRegister() >= int()

Does anybody know how to resolve this? Thanks.

Edit: This is the code I tried to run, which I just copied from a tutorial:

import numpy as np
from qiskit import QuantumCircuit, ClassicalRegister, QuantumRegister
from qiskit import execute

# Create a Quantum Register with 3 qubits.
q = QuantumRegister(3, 'q')

# Create a Quantum Circuit acting on the q register
circ = QuantumCircuit(q)

# Add a H gate on qubit 0, putting this qubit in superposition.
# Add a CX (CNOT) gate on control qubit 0 and target qubit 1, putting
# the qubits in a Bell state.
circ.cx(q[0], q[1])
# Add a CX (CNOT) gate on control qubit 0 and target qubit 2, putting
# the qubits in a GHZ state.
circ.cx(q[0], q[2])

# Import Aer
from qiskit import BasicAer

# Run the quantum circuit on a statevector simulator backend
backend = BasicAer.get_backend('statevector_simulator')

# Create a Quantum Program for execution
job = execute(circ, backend)

result = job.result()

outputstate = result.get_statevector(circ, decimals=3)
  • $\begingroup$ Can you include the running code? $\endgroup$
    – cnada
    Commented Jan 10, 2019 at 10:23
  • 1
    $\begingroup$ To second James' answer, I would recommend if you are still having problems to install Qiskit in a virtual environment via the Conda route on the installation guide. I've seen many issues with colleagues from dependency clashes. $\endgroup$ Commented Jan 10, 2019 at 15:32

1 Answer 1


The code you provide works fine for me, so I guess that something is wrong with your installation.

I recommend running the command

pip uninstall qiskit

and also

pip uninstall qiskit-terra
pip uninstall qiskit-aqua
pip uninstall qiskit-aer

and then reinstalling with

pip install qiskit

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