chore: add trailing-whitespace precommit

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -3,14 +3,14 @@ description: Report to help us reproduce the bug
 title: "[Bug]: "
 
 body:
-- type: markdown 
+- type: markdown
   attributes:
     value: >
         ## Thanks for taking the time to fill out this report
-- type: markdown 
+- type: markdown
   attributes:
     value: >
-       ### Before submitting a bug, please make sure it has not been reported in the 
+       ### Before submitting a bug, please make sure it has not been reported in the
        [list of issues](https://github.com/narwhals-dev/narwhals/issues).
 - type: textarea
   attributes:
@@ -25,7 +25,7 @@ body:
     description: |
        Please add a minimal code example to reproduce the bug.
   validations:
-       required: true 
+       required: true
 - type: textarea
   attributes:
     label: Expected results
@@ -39,7 +39,7 @@ body:
   attributes:
     label: Actual results
     description: |
-      Please paste or describe the results you observe instead of the expected results. 
+      Please paste or describe the results you observe instead of the expected results.
   validations:
     required: true
 - type: textarea

.github/ISSUE_TEMPLATE/config.yml

@@ -1,9 +1,8 @@
 contact_links:
 - name: Discord server
   url: https://discord.gg/V3PqtB4VA4
-  about: | 
+  about: |
       Developers and users can be found on the Discord server.
-      Please note that GitHub Discussions should be used in most cases instead.  
+      Please note that GitHub Discussions should be used in most cases instead.
 - name: Blank issue
   url: https://github.com/narwhals-dev/narwhals/issues/new
-

.github/ISSUE_TEMPLATE/doc_issue.yml

@@ -5,17 +5,17 @@ title: "[Doc]: "
 body:
 - type: markdown
   attributes:
-    value: > 
+    value: >
          ## Thanks for taking the time to fill out this form
 - type: dropdown
   id: TYPE
   attributes:
     label: What type of report is this?
-    options: 
+    options:
       - 'Correction'
       - 'Improvement'
   validations:
-      required: true  
+      required: true
 - type: textarea
   attributes:
     label: Please describe the issue.
@@ -30,6 +30,5 @@ body:
       How can we improve it
 - type: markdown
   attributes:
-    value: > 
+    value: >
         ### If you'd be interested in opening a pull request to fix this, please let us know!
-

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -3,19 +3,19 @@ description: Form to request a new feature
 title: "[Enh]: "
 
 body:
-- type: markdown 
+- type: markdown
   attributes:
     value: >
         ## Thanks for helping us improve Narwhals!
-- type: markdown 
+- type: markdown
   attributes:
     value: >
-       ### Before submitting a request, please check if it has already been discussed in the  
+       ### Before submitting a request, please check if it has already been discussed in the
        [list of issues](https://github.com/narwhals-dev/narwhals/issues?q=is%3Aissue+is%3Aclosed%2Bopen+).
 - type: textarea
   attributes:
     label: >
-       We would like to learn about your use case. For example, if this feature is needed 
+       We would like to learn about your use case. For example, if this feature is needed
        to adopt Narwhals in an open source project, could you please enter the link to it below?
     description: >
        Link to the project where this will be used if possible.
@@ -32,7 +32,7 @@ body:
     description: >
        Please suggest a solution if you can.
   validations:
-       required: false 
+       required: false
 - type: textarea
   attributes:
     label: If you have tried alternatives, please describe them below.
@@ -45,5 +45,5 @@ body:
        Context or useful information
 - type: markdown
   attributes:
-    value: > 
+    value: >
         ### If you'd be interested in opening a pull request to fix this, please let us know!

.github/pull_request_template.md

@@ -43,7 +43,7 @@ See [AI-assisted contributions](https://github.com/narwhals-dev/narwhals/blob/ma
 - [ ] Tests added
 - [ ] Documented the changes
 - [ ] If this is your first PR to narwhals, attach a screenshot of `pytest` passing locally (not CI):
-    
+
     ```bash
     PYTEST_ADDOPTS="--numprocesses=logical" \
     make run-ci DEPS="--extra pandas --extra dask --group core-tests --group sklearn --group plugins" \

.github/release-drafter.yml

@@ -5,7 +5,7 @@ exclude-labels:
 name-template: 'Narwhals unreleased'
 version-template: unreleased
 
-change-template: '- $TITLE (#$NUMBER)' 
+change-template: '- $TITLE (#$NUMBER)'
 
 categories:
   - title: 🏆 Highlights

.github/workflows/downstream_tests.yml

@@ -380,7 +380,7 @@ jobs:
       - name: Run tests
         run: |
           cd hierarchicalforecast
-          pytest tests --no-cov --import-mode=importlib 
+          pytest tests --no-cov --import-mode=importlib
 
 
   formulaic:

.github/workflows/pytest-ibis.yml

@@ -5,7 +5,7 @@ on:
     paths:
       - src/narwhals/_expression_parsing.py
       - src/narwhals/_ibis/**
-      - src/narwhals/_sql/**      
+      - src/narwhals/_sql/**
       - tests/**
       - .github/workflows/pytest-ibis.yml
       - pyproject.toml

.pre-commit-config.yaml

@@ -130,3 +130,9 @@ repos:
   -   id: no-commit-to-branch
   -   id: end-of-file-fixer
       exclude: .svg$
+  -   id: trailing-whitespace
+      exclude: |
+        (?x)^(
+            tests/data/.*\.csv|
+            .*\.svg
+        )$

CONTRIBUTING.md

@@ -66,7 +66,7 @@ Fork the repository by clicking on the fork button. You can find it in the right
 
 ### 3. Clone the repository
 
-Go to the forked repository on your GitHub account - you'll find it on your account in the tab Repositories. 
+Go to the forked repository on your GitHub account - you'll find it on your account in the tab Repositories.
 Click on the green `Code` button and then click the `Copy url to clipboard` icon.
 Open a terminal, choose the directory where you would like to have Narwhals repository and run the following git command:
 
@@ -96,7 +96,7 @@ git fetch upstream
 Check to see the remote has been added with `git remote -v`, you should see something like this:
 
 ```bash
-git remote -v                                                          
+git remote -v
 origin   git@github.com:YOUR-GITHUB-USERNAME/narwhals.git (fetch)
 origin   git@github.com:YOUR-GITHUB-USERNAME/narwhals.git (push)
 upstream git@github.com:narwhals-dev/narwhals.git (fetch)
@@ -210,24 +210,24 @@ We aim to use three standard patterns for handling test failures:
 
 Note: While we're not currently totally consistent with these patterns, any efforts towards our aim are appreciated and welcome.
 
-1. `requests.applymarker(pytest.mark.xfail)`: Used for features that are planned but not yet supported. 
-   
+1. `requests.applymarker(pytest.mark.xfail)`: Used for features that are planned but not yet supported.
+
    ```python
    def test_future_feature(request):
        request.applymarker(pytest.mark.xfail)
        # Test implementation for planned feature
    ```
 
 2. `pytest.mark.skipif`: Used when there's a condition under which the test cannot run (e.g., unsupported pandas versions).
-   
+
    ```python
    @pytest.mark.skipif(PANDAS_VERSION < (2, 0), reason="requires pandas 2.0+")
    def test_version_dependent():
        # Test implementation
    ```
 
 3. `pytest.raises`: Used for testing that code raises expected exceptions.
-   
+
    ```python
    def test_invalid_input():
        with pytest.raises(ValueError, match="expected error message"):
@@ -418,12 +418,12 @@ The aim is to keep maintainer time focused on review quality, not on triaging ma
     **This applies whether or not AI was used.**
 
 4. **First-time contributors** are asked to:
-    
+
     - Post a screenshot of the test suite passing locally (not on CI) in the PR description.
       This is a quick check that your dev environment works and that you have run the code you are proposing.
     - Keep at most one open pull request at a time, so reviewers can give it proper attention before
       you open the next one.
-  
+
 5. When interacting in issues, pull requests, discussion, discord, etc., **do not use LLMs to speak for you**,
     except for translation or grammar edits. Human-to-human communication is foundational to open source communities.
 

README.md

@@ -275,25 +275,25 @@ Narwhals has been featured in several talks, podcasts, and blog posts:
 - [Python Bytes Podcast](https://www.youtube.com/live/N7w_ESVW40I?si=y-wN1uCsAuJOKlOT&t=382)
   Episode 402, topic #2
 
-- [Super Data Science: ML & AI Podcast](https://www.youtube.com/watch?v=TeG4U8R0U8U)  
+- [Super Data Science: ML & AI Podcast](https://www.youtube.com/watch?v=TeG4U8R0U8U)
   Narwhals: For Pandas-to-Polars DataFrame Compatibility
 
-- [Sample Space Podcast | probabl](https://youtu.be/8hYdq4sWbbQ?si=WG0QP1CZ6gkFf18b)  
+- [Sample Space Podcast | probabl](https://youtu.be/8hYdq4sWbbQ?si=WG0QP1CZ6gkFf18b)
   How Narwhals has many end users ... that never use it directly. - Marco Gorelli
 
 - [The Real Python Podcast](https://www.youtube.com/watch?v=w5DFZbFYzCM)
   Narwhals: Expanding DataFrame Compatibility Between Libraries
 
-- [Pycon Lithuania 2024](https://www.youtube.com/watch?v=-mdx7Cn6_6E)  
+- [Pycon Lithuania 2024](https://www.youtube.com/watch?v=-mdx7Cn6_6E)
   Marco Gorelli - DataFrame interoperatiblity - what's been achieved, and what comes next?
 
-- [Pycon Italy 2024](https://www.youtube.com/watch?v=3IqUli9XsmQ)  
+- [Pycon Italy 2024](https://www.youtube.com/watch?v=3IqUli9XsmQ)
   How you can write a dataframe-agnostic library - Marco Gorelli
 
-- [Polars Blog Post](https://pola.rs/posts/lightweight_plotting/)  
+- [Polars Blog Post](https://pola.rs/posts/lightweight_plotting/)
   Polars has a new lightweight plotting backend
 
-- [Quansight Labs blog post (w/ Scikit-Lego)](https://labs.quansight.org/blog/scikit-lego-narwhals)  
+- [Quansight Labs blog post (w/ Scikit-Lego)](https://labs.quansight.org/blog/scikit-lego-narwhals)
   How Narwhals and scikit-lego came together to achieve dataframe-agnosticism
 
 ## Why "Narwhals"?

docs/api-reference/typing.md

@@ -69,7 +69,7 @@ reveal_type(func_2(df))
 
 Running `mypy` on it gives:
 ```console
-$ mypy t.py 
+$ mypy t.py
 t.py:13: note: Revealed type is "polars.dataframe.frame.DataFrame"
 t.py:21: note: Revealed type is "Any"
 Success: no issues found in 1 source file

docs/concepts/null_handling.md

@@ -3,10 +3,10 @@
 ## TL;DR
 
 All dataframe tools, except for those which piggy-back off of pandas, make a clear
-distinction between NaN and null values. 
+distinction between NaN and null values.
 
 !!! tip
-    **We recommend only handling null values in applications and leaving NaN values as an 
+    **We recommend only handling null values in applications and leaving NaN values as an
     edge case resulting from users having performed undefined mathematical operations.**
 
 ## What's the difference?

docs/extending.md

@@ -5,7 +5,7 @@
     The extension mechanism in Narwhals is experimental and under development.
     If anything is not clear, or doesn't work, please do raise an issue or
     contact us on Discord (see the link on the README).
-  
+
 If you would like to make a new library Narwhals-compatible, then there are
 three ways to go about it:
 
@@ -45,18 +45,18 @@ handle plugins. For this integration to work, any plugin architecture must conta
     own library name, for example `narwhals-grizzlies = 'narwhals_grizzlies'`
 
   2. a top-level `__init__.py` file containing the following:
-  
+
     - `is_native` and `__narwhals_namespace__` functions.
     - a string constant `NATIVE_PACKAGE` which holds the name of the library for which the plugin is made.
 
-    `is_native` accepts a native object and returns a boolean indicating whether the native object is 
+    `is_native` accepts a native object and returns a boolean indicating whether the native object is
     a dataframe of the library the plugin was written for.
 
     `__narwhals_namespace__` takes the Narwhals version and returns a compliant namespace for the library,
-    i.e. one that complies with the CompliantNamespace protocol. This protocol specifies a `from_native` 
+    i.e. one that complies with the CompliantNamespace protocol. This protocol specifies a `from_native`
     function, whose input parameter is the Narwhals version and which returns a compliant Narwhals LazyFrame
-    which wraps the native dataframe. 
-  
+    which wraps the native dataframe.
+
     Take a look at the `Plugin` protocol in `narwhals/plugins.py` for the
     signatures.
 

docs/how_it_works.md

@@ -88,7 +88,7 @@ Recall from above that an expression is a function from a dataframe to a sequenc
 The `_call` method gives us that function! Let's see it in action.
 
 Note: the following examples use `PandasLikeDataFrame` and `PandasLikeSeries`. These are backed
-by actual `pandas.DataFrame`s and `pandas.Series` respectively and are Narwhals-compliant. We can access the 
+by actual `pandas.DataFrame`s and `pandas.Series` respectively and are Narwhals-compliant. We can access the
 underlying pandas objects via `PandasLikeDataFrame._native_frame` and `PandasLikeSeries._native_series`.
 
 ```python exec="yes" result="python" session="pandas_impl" source="above"
@@ -347,7 +347,7 @@ Here's a brief description of each piece of metadata:
 
 - `has_windows`: Whether the expression already contains an `over(...)` statement.
 - `n_orderable_ops`: How many order-dependent operations the expression contains.
-  
+
     Examples:
 
     - `nw.col('a')` contains 0 orderable operations.

docs/javascripts/extra.js

@@ -8,10 +8,10 @@
 
 function cleanupClipboardText(targetSelector) {
     const targetElement = document.querySelector(targetSelector);
-  
+
     // exclude "Generic Prompt" and "Generic Output" spans from copy
     const excludedClasses = ["gp", "go"];
-  
+
     const clipboardText = Array.from(targetElement.childNodes)
       .filter(
         (node) =>
@@ -23,7 +23,7 @@ function cleanupClipboardText(targetSelector) {
       .filter((s) => s !== "");
     return clipboardText.join("").trim();
   }
-  
+
   // Sets copy text to attributes lazily using an Intersection Observer.
   function setCopyText() {
     // The `data-clipboard-text` attribute allows for customized content in the copy
@@ -33,11 +33,11 @@ function cleanupClipboardText(targetSelector) {
     const elements = document.querySelectorAll(
       'button[data-clipboard-target$="code"]',
     );
-  
+
     if (elements.length === 0) {
       return;
     }
-  
+
     const observer = new IntersectionObserver((entries) => {
       entries.forEach((entry) => {
         // target in the viewport that have not been patched
@@ -51,17 +51,16 @@ function cleanupClipboardText(targetSelector) {
         }
       });
     });
-  
+
     elements.forEach((elt) => {
       observer.observe(elt);
     });
   }
-  
+
   // Using the document$ observable is particularly important if you are using instant loading since
   // it will not result in a page refresh in the browser
   // See `How to integrate with third-party JavaScript libraries` guideline:
   // https://squidfunk.github.io/mkdocs-material/customization/?h=javascript#additional-javascript
   document$.subscribe(function () {
     setCopyText();
   });
-

docs/javascripts/katex.js

@@ -1,4 +1,4 @@
-document$.subscribe(({ body }) => { 
+document$.subscribe(({ body }) => {
     renderMathInElement(body, {
       delimiters: [
         { left: "$$",  right: "$$",  display: true },