Fix duplicate HTML when map.save() is called repeatedly

Repeated render() calls accumulated script/header/html content because
render helpers created new child elements with unique IDs on each pass.
Reset figure output sections before rendering and use stable script names
for SetIcon and ElementAddToElement.

Fixes #2237

Author: vraj2131

folium/__init__.py

@@ -4,7 +4,6 @@
     CssLink,
     Div,
     Element,
-    Figure,
     Html,
     IFrame,
     JavascriptLink,
@@ -29,6 +28,7 @@
     Vega,
     VegaLite,
 )
+from folium.figure import Figure
 from folium.folium import Map
 from folium.map import (
     FeatureGroup,

folium/elements.py

@@ -149,6 +149,18 @@ def __init__(self, element_name: str, element_parent_name: str):
         self.element_name = element_name
         self.element_parent_name = element_parent_name
 
+    def render(self, **kwargs):
+        figure = self.get_root()
+        assert isinstance(
+            figure, Figure
+        ), "You cannot render this Element if it is not in a Figure."
+        script = self._template.module.__dict__.get("script", None)
+        if script is not None:
+            figure.script.add_child(
+                Element(script(self, kwargs)),
+                name=f"{self.element_name}_add_to_{self.element_parent_name}",
+            )
+
 
 class IncludeStatement(MacroElement):
     """Generate an include statement on a class."""

folium/figure.py

@@ -0,0 +1,23 @@
+"""Folium-specific Figure subclass."""
+
+from branca.element import Figure as BrancaFigure
+
+
+class Figure(BrancaFigure):
+    """Figure that supports repeated rendering without duplicating output.
+
+    Branca elements populate ``header``, ``html``, and ``script`` during
+    ``render()``. Some folium elements create new child nodes on every render
+    call, which causes repeated ``save()`` calls to accumulate duplicate HTML
+    and JavaScript. Clearing the rendered sections before each render makes
+    output idempotent while preserving static header content from ``__init__``.
+    """
+
+    def render(self, **kwargs):
+        meta = self.header._children.pop("meta_http", None)
+        self.header._children.clear()
+        if meta is not None:
+            self.header._children["meta_http"] = meta
+        self.html._children.clear()
+        self.script._children.clear()
+        return super().render(**kwargs)

folium/folium.py

@@ -8,9 +8,10 @@
 from collections.abc import Sequence
 from typing import Any, Optional, Union
 
-from branca.element import Element, Figure
+from branca.element import Element
 
 from folium.elements import JSCSSMixin
+from folium.figure import Figure
 from folium.map import Evented, FitBounds, Layer
 from folium.raster_layers import TileLayer
 from folium.template import Template

folium/map.py

@@ -517,6 +517,18 @@ def __init__(
             self.marker = marker
             self.icon = icon
 
+        def render(self, **kwargs):
+            figure = self.get_root()
+            assert isinstance(
+                figure, Figure
+            ), "You cannot render this Element if it is not in a Figure."
+            script = self._template.module.__dict__.get("script", None)
+            if script is not None:
+                figure.script.add_child(
+                    Element(script(self, kwargs)),
+                    name=f"{self.marker.get_name()}_set_icon",
+                )
+
     def __init__(
         self,
         location: Optional[Sequence[float]] = None,
@@ -557,7 +569,7 @@ def render(self):
                 f"{self._name} location must be assigned when added directly to map."
             )
         if self.icon:
-            self.add_child(self.SetIcon(marker=self, icon=self.icon))
+            self.add_child(self.SetIcon(marker=self, icon=self.icon), name="set_icon")
         super().render()
 
     def set_icon(self, icon):

folium/plugins/dual_map.py

@@ -1,6 +1,7 @@
-from branca.element import Figure, MacroElement
+from branca.element import MacroElement
 
 from folium.elements import EventHandler, JSCSSMixin
+from folium.figure import Figure
 from folium.folium import Map
 from folium.map import LayerControl
 from folium.template import Template

tests/test_map.py

@@ -290,3 +290,27 @@ def test_icon_invalid_marker_colors():
     pytest.warns(UserWarning, Icon, color="lila")
     pytest.warns(UserWarning, Icon, color=42)
     pytest.warns(UserWarning, Icon, color=None)
+
+
+def test_repeated_save_produces_identical_html(tmp_path):
+    """Regression test for https://github.com/python-visualization/folium/issues/2237"""
+    m = Map(location=[40.75, -73.98], zoom_start=13)
+    locations = [
+        [40.7829, -73.9654],
+        [40.7484, -73.9857],
+        [40.7580, -73.9855],
+    ]
+    for lat, lon in locations:
+        Marker([lat, lon], icon=Icon(color="blue", icon="info-sign")).add_to(m)
+
+    path1 = tmp_path / "1.html"
+    path2 = tmp_path / "2.html"
+    path3 = tmp_path / "3.html"
+    m.save(path1)
+    m.save(path2)
+    m.save(path3)
+
+    html1 = path1.read_text()
+    html2 = path2.read_text()
+    html3 = path3.read_text()
+    assert html1 == html2 == html3