From 64a40938de001ea57e8384bccd46ea0d24bc4b05 Mon Sep 17 00:00:00 2001
From: Marco Gorelli <33491632+MarcoGorelli@users.noreply.github.com>
Date: Sun, 17 Mar 2024 15:17:09 +0000
Subject: [PATCH] extending

---
 docs/extending.md     | 2 ++
 mkdocs.yml            | 1 +
 narwhals/dataframe.py | 3 +++
 3 files changed, 6 insertions(+)
 create mode 100644 docs/extending.md

diff --git a/docs/extending.md b/docs/extending.md
new file mode 100644
index 000000000..f398cd864
--- /dev/null
+++ b/docs/extending.md
@@ -0,0 +1,2 @@
+# How Narwhals can support your dataframe as well!
+
diff --git a/mkdocs.yml b/mkdocs.yml
index 064c8fe5b..ae63173b0 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -8,6 +8,7 @@ nav:
     - basics/dataframe.md
     - basics/column.md
     - basics/complete_example.md
+  - Extending: extending.md
   - API Reference: reference.md
 theme:
   name: material
diff --git a/narwhals/dataframe.py b/narwhals/dataframe.py
index 625f8c83d..ef00cb134 100644
--- a/narwhals/dataframe.py
+++ b/narwhals/dataframe.py
@@ -177,6 +177,9 @@ def __init__(
         ):  # pragma: no cover
             self._dataframe = PandasDataFrame(df, implementation="cudf")
             self._implementation = "cudf"
+        elif hasattr(df, "__narwhals_dataframe__"):
+            self._dataframe = df.__narwhals_dataframe__()
+            self._implementation = "custom"
         else:
             msg = f"Expected pandas-like dataframe, Polars dataframe, or Polars lazyframe, got: {type(df)}"
             raise TypeError(msg)