---
title: map_fermion_action_generators (latest version)
description: API reference for qiskit_fermions.mappers.map_fermion_action_generators in the latest version of qiskit-fermions
source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit-fermions/mappers-map-fermion-action-generators
---

# map\_fermion\_action\_generators

`map_fermion_action_generators(operator, map_action, identity, compose=None)`

Map a [`FermionOperator`](/docs/api/qiskit-fermions/operators-fermion-operator "qiskit_fermions.operators.FermionOperator") to another operator type.

This is a generic function to aid in implementing new mappers for [`FermionOperator`](/docs/api/qiskit-fermions/operators-fermion-operator "qiskit_fermions.operators.FermionOperator") instances. At its core, it simply iterates over the terms of the operator, mapping each encountered [`FermionAction`](/docs/api/qiskit-fermions/operators-fermion-action-fermion-action "qiskit_fermions.operators.fermion_action.FermionAction") with the user-provided `map_action` function. In combination with the user-provided `identity` generator, this allows mapping to arbitrary output types.

> **Note**
>
> The output type `T` must support multiplication by a scalar via `__mul__`. If `compose=None` it must also support composition of two instances via `__and__`.

```pycon
>>> from qiskit_fermions.mappers import map_fermion_action_generators
>>> from qiskit_fermions.operators import FermionAction, FermionOperator, ann, cre
>>> from qiskit.quantum_info import SparsePauliOp
>>>
>>> def jordan_wigner(action: FermionAction) -> SparsePauliOp:
...     act, idx = action
...     qubits = list(range(idx + 1))
...     return SparsePauliOp.from_sparse_list(
...         [
...             ("Z" * idx + "X", qubits, 0.5),
...             ("Z" * idx + "Y", qubits, -0.5j if act else 0.5j),
...         ],
...         num_qubits=num_qubits,
...     )
>>>
>>> num_qubits = 2
>>> def identity() -> SparsePauliOp:
...     return SparsePauliOp.from_sparse_list([("", [], 1)], num_qubits)
>>>
>>> op = FermionOperator.from_dict({(cre(0), ann(1)): 2.0})
>>> qop = map_fermion_action_generators(op, jordan_wigner, identity)
>>> print([(label, complex(coeff)) for label, coeff in sorted(qop.label_iter())])
[('II', 0j), ('XX', (0.5+0j)), ('XY', -0.5j), ('YX', 0.5j), ('YY', (0.5+0j))]
```

**Parameters**

- **operator** ([*FermionOperator*](/docs/api/qiskit-fermions/operators-fermion-operator "qiskit_fermions.operators.fermion_operator.FermionOperator")) – the operator to be mapped.
- **map\_action** ([*Callable*](https://docs.python.org/3/library/collections.abc.html#collections.abc.Callable)*\[\[*[*tuple*](https://docs.python.org/3/library/stdtypes.html#tuple)*\[*[*bool*](https://docs.python.org/3/library/functions.html#bool)*,* [*int*](https://docs.python.org/3/library/functions.html#int)*]], T]*) – the function to map a single [`FermionAction`](/docs/api/qiskit-fermions/operators-fermion-action-fermion-action "qiskit_fermions.operators.fermion_action.FermionAction") to the desired output type.
- **identity** ([*Callable*](https://docs.python.org/3/library/collections.abc.html#collections.abc.Callable)*\[\[], T]*) – the function to generate the multiplicative identity instance of the output type.
- **compose** ([*Callable*](https://docs.python.org/3/library/collections.abc.html#collections.abc.Callable)*\[\[T, T], T] | None*) – an optional function to implement the compositiion logic of two output type instances. If this is not provided, it will default to using [`operator.and_()`](https://docs.python.org/3/library/operator.html#operator.and_).

**Returns**

The mapped operator.

**Return type**

*T*