# qiskit.opflow.converters

## Converters

`qiskit.opflow.converters`

The `qiskit.opflow`

module is deprecated and will be removed no earlier than 3 months after the release date. For code migration guidelines, visit https://qisk.it/opflow_migration.

Converters are objects which manipulate Operators, usually traversing an Operator to change certain sub-Operators into a desired representation. Often the converted Operator is isomorphic or approximate to the original Operator in some way, but not always. For example, a converter may accept `CircuitOp`

and return a `SummedOp`

of `PauliOp`

’s representing the circuit unitary. Converters may not have polynomial space or time scaling in their operations. On the contrary, many converters, such as a `MatrixExpectation`

or `MatrixEvolution`

, which convert `PauliOp`

’s to `MatrixOp`

’s internally, will require time or space exponential in the number of qubits unless a clever trick is known (such as the use of sparse matrices).

Not all converters are in this module, as `expectations`

and `evolutions`

are also converters.

### Converter Base Class

The converter base class simply enforces the presence of a `convert()`

method.

`ConverterBase` () | Deprecated: Converters take an Operator and return a new Operator, generally isomorphic in some way with the first, but with certain desired properties. |

### Converters

In addition to the base class, directory holds a few miscellaneous converters which are used frequently around the Operator flow.

`CircuitSampler` (backend[, statevector, ...]) | Deprecated: The CircuitSampler traverses an Operator and converts any CircuitStateFns into approximations of the state function by a DictStateFn or VectorStateFn using a quantum backend. |

`AbelianGrouper` ([traverse]) | Deprecated: The AbelianGrouper converts SummedOps into a sum of Abelian sums. |

`DictToCircuitSum` ([traverse, convert_dicts, ...]) | Deprecated: Converts `DictStateFns` or `VectorStateFns` to equivalent `CircuitStateFns` or sums thereof. |

`PauliBasisChange` ([destination_basis, ...]) | Deprecated: Converter for changing Paulis into other bases. |

`TwoQubitReduction` (num_particles) | Deprecated: Two qubit reduction converter which eliminates the central and last qubit in a list of Pauli that has diagonal operators (Z,I) at those positions. |