Remove Python 3.9 in favour of 3.10 as minimum (#6223)

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- [x] All new features must include a unit test.
If you've fixed a bug or added code that should be tested, add a test to
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      test directory!

- [x] All new functions and code must be clearly commented and
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If you do make documentation changes, make sure that the docs build and
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- [x] Ensure that the test suite passes, by running `make test`.

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      change, and including a link back to the PR.

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------------------------------------------------------------------------------------------------------------

**Context:** Remove Py 3.9 from the CI runners and package metadata.

**Description of the Change:**

**Benefits:**

**Possible Drawbacks:**

**Related GitHub Issues:**

.github/workflows/format.yml

@@ -22,7 +22,7 @@ jobs:
  - name: Set up Python
  uses: actions/setup-python@v2
  with:
- python-version: 3.9
+ python-version: "3.10"
 
  - name: Install dependencies
  run: pip install black pylint==2.7.4 isort==5.13.2
@@ -31,13 +31,13 @@ jobs:
 
  - name: Run Black
  run: |
- black -t py39 -t py310 -t py311 -l 100 pennylane/ --check
- black -t py39 -t py310 -t py311 -l 100 tests/ --check
+ black -t py310 -t py311 -t py312 -l 100 pennylane/ --check
+ black -t py310 -t py311 -t py312 -l 100 tests/ --check
 
  - name: Run isort
  run: |
- isort --py 311 --profile black -l 100 -o autoray -p ./pennylane --skip __init__.py --filter-files ./pennylane --check
- isort --py 311 --profile black -l 100 -o autoray -p ./pennylane --skip __init__.py --filter-files ./tests --check
+ isort --py 312 --profile black -l 100 -o autoray -p ./pennylane --skip __init__.py --filter-files ./pennylane --check
+ isort --py 312 --profile black -l 100 -o autoray -p ./pennylane --skip __init__.py --filter-files ./tests --check
 
  - name: Run Pylint (source files)
  if: always()

.github/workflows/install_deps/action.yml

@@ -7,7 +7,7 @@ inputs:
  python_version:
  description: The version of Python to use in order to run unit tests
  required: false
- default: '3.9'
+ default: '3.10'
  install_jax:
  description: Indicate if JAX should be installed or not
  required: false

.github/workflows/interface-unit-tests.yml

@@ -25,7 +25,7 @@ on:
  Indicate if a lightened version of the CI should be run instead of the entire suite.
 
  The lightened version of the CI includes the following changes:
- - Only Python 3.9 is tested against, instead of 3.9, 3.10, 3.11, 3.12
+ - Only Python 3.10 is tested against, instead of 3.10, 3.11, 3.12
  required: false
  type: boolean
  default: false
@@ -63,23 +63,23 @@ jobs:
  then
  cat >python_versions.json <<-EOF
  {
- "default": ["3.9"]
+ "default": ["3.10"]
  }
  EOF
  else
  cat >python_versions.json <<-EOF
  {
- "default": ["3.9", "3.10", "3.11", "3.12"],
- "torch-tests": ["3.9", "3.11"],
- "tf-tests": ["3.9", "3.11"],
- "jax-tests": ["3.9", "3.12"],
- "all-interfaces-tests": ["3.9"],
- "external-libraries-tests": ["3.9"],
- "qcut-tests": ["3.9"],
- "qchem-tests": ["3.9"],
- "gradients-tests": ["3.9"],
- "data-tests": ["3.9", "3.10"],
- "device-tests": ["3.9"]
+ "default": ["3.10", "3.11", "3.12"],
+ "torch-tests": ["3.10", "3.12"],
+ "tf-tests": ["3.10", "3.12"],
+ "jax-tests": ["3.10", "3.12"],
+ "all-interfaces-tests": ["3.10"],
+ "external-libraries-tests": ["3.10"],
+ "qcut-tests": ["3.10"],
+ "qchem-tests": ["3.10"],
+ "gradients-tests": ["3.10"],
+ "data-tests": ["3.10"],
+ "device-tests": ["3.10"]
  }
  EOF
  fi

.github/workflows/tests-gpu.yml

@@ -40,9 +40,9 @@ jobs:
  max-parallel: 2
  matrix:
  python-version:
- - 3.9
  - '3.10'
  - '3.11'
+ - '3.12'
 
  env:
  SUITE: gpu

.github/workflows/unit-test.yml

@@ -23,7 +23,7 @@ on:
  description: The version of Python to use in order to run unit tests
  required: false
  type: string
- default: '3.9'
+ default: '3.10'
  pipeline_mode:
  description: The pipeline mode can be unit-tests, benchmarks, or reference-benchmark
  required: false

.github/workflows/upload.yml

@@ -24,7 +24,7 @@ jobs:
  - name: Set up Python
  uses: actions/setup-python@v2
  with:
- python-version: 3.9
+ python-version: "3.10"
 
  - name: Build PennyLane wheel
  run: |

.readthedocs.yml

@@ -8,7 +8,7 @@ version: 2
 build:
  os: ubuntu-22.04
  tools:
- python: "3.9"
+ python: "3.10"
  apt_packages:
  - graphviz
 

README.md

@@ -67,7 +67,7 @@
 
 ## Installation
 
-PennyLane requires Python version 3.9 and above. Installation of PennyLane, as well as all
+PennyLane requires Python version 3.10 and above. Installation of PennyLane, as well as all
 dependencies, can be done using pip:
 
 ```console

doc/releases/changelog-dev.md

@@ -22,6 +22,9 @@
 
 <h3>Breaking changes 💔</h3>
 
+* Remove support for Python 3.9.
+ [(#6223)](https://github.com/PennyLaneAI/pennylane/pull/6223)
+
 * `DefaultQubitTF` is removed. Please use `default.qubit` for all interfaces.
  [(#6207)](https://github.com/PennyLaneAI/pennylane/pull/6207)
 
@@ -62,3 +65,4 @@ Guillermo Alonso
 Utkarsh Azad
 Christina Lee
 William Maxwell
+Lee J. O'Riordan

setup.py

@@ -85,7 +85,6 @@
  "Operating System :: Microsoft :: Windows",
  "Programming Language :: Python",
  "Programming Language :: Python :: 3",
- "Programming Language :: Python :: 3.9",
  "Programming Language :: Python :: 3.10",
  "Programming Language :: Python :: 3.11",
  "Programming Language :: Python :: 3.12",