Necessary updates for using pixi

_episodes/07-development-setup.md

@@ -2,7 +2,7 @@
 title: "Development and contribution"
 teaching: 10
 exercises: 20
-compatibility: ESMValTool v2.14.0
+compatibility: ESMValTool v2.15.0
 
 questions:
 - "What is a development installation?"
@@ -109,73 +109,46 @@ nothing to commit, working tree clean
 ~~~
 {: .output}
 
-### 2 ESMValTool dependencies
-
-Please don’t forget if an esmvaltool environment is already created
-following the lesson
-[Installation]({{ page.root }}{% link _episodes/02-installation.md %}),
-we should choose another name for the new environment in this lesson.
-
-ESMValTool uses `mamba` for the recommended installation.
-For a minimal mamba installation, see section **Install Mamba** in lesson
-[Installation]({{ page.root }}{% link _episodes/02-installation.md %}).
-
-It is good practice to update the version of mamba on your machine before
-setting up ESMValTool. This can be done as follows:
-
-~~~bash
-mamba update --name base mamba conda
-~~~
-
-To simplify the installation process, an environment file ``environment.yml`` is
-provided in the ESMValTool directory. We create an environment by running:
-
-~~~bash
-mamba env create --name esmvaltool --file environment.yml
-~~~
-
-The environment is called ``esmvaltool`` by default.
-If an ``esmvaltool`` environment is already created following the lesson
-[Installation]({{ page.root }}{% link _episodes/02-installation.md %}),
-we should choose another name for the new environment in this lesson by:
+### 2 ESMValTool installation
 
+It is recommended to use [pixi](https://pixi.prefix.dev/) to manage ESMValTool 
+dependencies. There are different ways to install pixi which you can find on the  
+[pixi installation instructions](https://pixi.prefix.dev/latest/installation/) 
+website. One way to install pixi is for example:
 ~~~bash
-mamba env create --name a_new_name --file environment.yml
+curl -fsSL https://pixi.sh/install.sh | sh
 ~~~
-This will create a new conda environment and install ESMValTool (with all
-dependencies that are needed for development purposes) into it with a single command.
-
-For more information see 
-[Mamba User Guide](https://mamba.readthedocs.io/en/latest/user_guide/mamba.html).
-
-Now, we should activate the environment:
 
+After installing pixi you run the following command to install all of the 
+required dependencies for running and developing Python diagnostics:
 ~~~bash
-conda activate esmvaltool
+pixi shell --frozen
 ~~~
-where ``esmvaltool`` is the name of the environment (replace by ``a_new_name``
-in case another environment name was used).
-
-### 3 ESMValTool installation
-
-ESMValTool can be installed in a ``develop`` mode by running:
+Using the '--frozen' flag instructs pixi to use the versions of the packages 
+listed in the ``pixi.lock`` file. Using this option makes all pixi 
+commands run faster and makes your analyses more reproducible.
 
+As we want to add new code later in the epsiode, we want to install ``pre-commit``.
+This will make sure that our changes will be formatted correctly when we commit 
+them.
 ~~~bash
-pip install --no-deps --editable '.[develop]'
+pre-commit install
 ~~~
 
-This will add the ``esmvaltool`` directory to the Python path in editable mode and
-install the development dependencies. We should check if the installation
-works properly. To do this, run the tool with:
+To check if the installation of pixi works properly, we run ESMValTool with:
 
 ~~~bash
 esmvaltool --help
 ~~~
 
 If the installation is successful, ESMValTool prints a help message to the console.
 
+Further information and instructions using pixi can be found in the [ESMValTool
+documentation](https://docs.esmvaltool.org/en/latest/quickstart/installation.html#install-from-source).
+And if you need to exit the pixi environment, run ``exit`` or ``Ctrl+D``.
+
 
-### 4 Updating ESMValTool
+### 3 Updating ESMValTool
 
 The ``main`` branch has the latest features of ESMValTool. Please make sure
 that the source code on your machine is up-to-date. If you obtain the source
@@ -249,9 +222,8 @@ no syntax errors in our recipes and config files
 - [lintr](https://github.com/jimhester/lintr) for diagnostic scripts written in R
 - [codespell](https://pypi.org/project/codespell/) to check grammar
 
-The good news is that ``pre-commit`` has been already installed
-when we chose development installation.
-``pre-commit`` is a command line and runs all of those tools. It also fixes some of those errors.
+The good news is that ``pre-commit`` which we already installed earlier is a command line 
+and runs all of those tools. It also fixes some of those errors.
 To explore other tools, have a look at ESMValTool documentation on
 [Code quality](https://docs.esmvaltool.org/en/latest/community/
 code_documentation.html#code-quality).