# Has \`qml.purity\` been deprecated?

**URL:** <https://discuss.pennylane.ai/t/has-qml-purity-been-deprecated/2605>\
**Category:** PennyLane Help\
**Created:** [February 21, 2023, 9:58pm UTC](https://discuss.pennylane.ai/t/has-qml-purity-been-deprecated/2605 "2023-02-21T21:58:26Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![diemilio](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/diemilio/32/1413_2.png) [@diemilio](https://discuss.pennylane.ai/u/diemilio)\
**Post date:** [February 21, 2023, 9:58pm UTC](https://discuss.pennylane.ai/t/has-qml-purity-been-deprecated/2605/1 "2023-02-21T21:58:26Z")

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In pennylane’s documentation you can find `qml.purity` under [`qml.measurements.purity`](https://docs.pennylane.ai/en/latest/code/api/pennylane.measurements.purity.html), where you can return the purity of a density matrix directly like this:

```python
dev = qml.device("default.mixed", wires=2)

@qml.qnode(dev)
def circuit_purity(p):
    qml.Hadamard(wires=0)
    qml.CNOT(wires=[0, 1])
    qml.BitFlip(p, wires=0)
    qml.BitFlip(p, wires=1)
    return qml.purity(wires=[0,1])

```

However, looking at the latest version of pennylane, this function doesn’t seem to be available. Only `pennylane.qinfo.transforms.purity()` and `pennylane.math.purity()` seem to be available, which require to pass a qnode or a state.

Has it been deprecated?

Thanks.

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**Author:** ![CatalinaAlbornoz](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/catalinaalbornoz/32/1196_2.png) [@CatalinaAlbornoz](https://discuss.pennylane.ai/u/CatalinaAlbornoz)\
**Post date:** [February 24, 2023, 11:57pm UTC](https://discuss.pennylane.ai/t/has-qml-purity-been-deprecated/2605/2 "2023-02-24T23:57:01Z")

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Hi @diemilio, it’s quite the opposite!

You’re probably looking at the [latest](https://docs.pennylane.ai/en/latest/introduction/measurements.html) version of the documentation, which is the development version. This includes a new feature which is being able to the purity as your measurement 🤩.

Please let me know if you find any issues with this!

However you’re probably using the current [stable](https://docs.pennylane.ai/en/stable/introduction/measurements.html) version of PennyLane, v0.28, which doesn’t include this feature.

You could use the latest [development version](https://pennylane.ai/install.html?version=preview) of PennyLane, or you could decide not to use this feature. We will release a new version of PennyLane on Tuesday so if this isn’t urgent you could wait until then too 🙂 .

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**Author:** ![diemilio](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/diemilio/32/1413_2.png) [@diemilio](https://discuss.pennylane.ai/u/diemilio)\
**Post date:** [March 5, 2023, 12:57pm UTC](https://discuss.pennylane.ai/t/has-qml-purity-been-deprecated/2605/3 "2023-03-05T12:57:28Z")

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Ah! Got it! Thanks so much for the help 🙂

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<div class="post-metadata">

**Author:** ![CatalinaAlbornoz](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/catalinaalbornoz/32/1196_2.png) [@CatalinaAlbornoz](https://discuss.pennylane.ai/u/CatalinaAlbornoz)\
**Post date:** [March 7, 2023, 5:21pm UTC](https://discuss.pennylane.ai/t/has-qml-purity-been-deprecated/2605/4 "2023-03-07T17:21:06Z")

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No problem @diemilio ! Let us know what you think of this feature. And remember to use v0.29.1 😃