Add support for rendering in pyodide/pyscript (#5338)

* Add support for rendering in pyodide/pyscript

* Update repr code

holoviews/__init__.py

@@ -1,4 +1,4 @@
-import os, io
+import io, os, sys
 
 import numpy as np # noqa (API import)
 import param
@@ -44,6 +44,9 @@ class notebook_extension(param.ParameterizedFunction):
         def __call__(self, *args, **opts): # noqa (dummy signature)
             raise Exception("IPython notebook not available: use hv.extension instead.")
 
+if '_pyodide' in sys.modules:
+    from .pyodide import pyodide_extension as extension # noqa (API import)
+
 # A single holoviews.rc file may be executed if found.
 for rcfile in [os.environ.get("HOLOVIEWSRC", ''),
                os.path.abspath(os.path.join(os.path.split(__file__)[0],

holoviews/pyodide.py

@@ -0,0 +1,92 @@
+import asyncio
+import sys
+
+from js import document
+
+from bokeh.embed.elements import script_for_render_items
+from bokeh.embed.util import standalone_docs_json_and_render_items
+from bokeh.embed.wrappers import wrap_in_script_tag
+from panel.io.pyodide import _link_docs
+from panel.pane import panel as as_panel
+
+from ..core.dimension import LabelledData
+from ..core.options import Store
+from ..util import extension as _extension
+
+
+#-----------------------------------------------------------------------------
+# Private API
+#-----------------------------------------------------------------------------
+
+async def _link(ref, doc):
+    from js import Bokeh
+    rendered = Bokeh.index.object_keys()
+    if ref not in rendered:
+        await asyncio.sleep(0.1)
+        await _link(ref, doc)
+        return
+    views = Bokeh.index.object_values()
+    view = views[rendered.indexOf(ref)]
+    _link_docs(doc, view.model.document)
+
+def render_html(obj):
+    if hasattr(sys.stdout, '_out'):
+        out = sys.stdout._out # type: ignore
+    else:
+        raise ValueError("Could not determine target node to write to.")
+    doc = Document() 
+    as_panel(obj).server_doc(doc, location=False)
+    docs_json, [render_item,] = standalone_docs_json_and_render_items(
+        doc.roots, suppress_callback_warning=True
+    )
+    for root in doc.roots:
+        render_item.roots._roots[root] = target
+    document.getElementById(target).classList.add('bk-root')
+    script = script_for_render_items(docs_json, [render_item])
+    asyncio.create_task(_link(doc.roots[0].ref['id'], doc))
+    return {'text/html': wrap_in_script_tag(script)}, {}
+
+def render_image(element, fmt):
+    """
+    Used to render elements to an image format (svg or png) if requested
+    in the display formats.
+    """
+    if fmt not in Store.display_formats:b
+        return None
+
+    backend = Store.current_backend
+    if type(element) not in Store.registry[backend]:
+        return None
+    renderer = Store.renderers[backend]
+    plot = renderer.get_plot(element)
+
+    # Current renderer does not support the image format
+    if fmt not in renderer.param.objects('existing')['fig'].objects:
+        return None
+
+    data, info = renderer(plot, fmt=fmt)
+    return {info['mime_type']: data}, {}
+
+def render_png(obj):
+    return render_image(element, 'png')
+
+def render_svg(obj):
+    return render_image(element, 'svg')
+
+
+#-----------------------------------------------------------------------------
+# Public API
+#-----------------------------------------------------------------------------
+
+class pyodide_extension(_extension):
+
+    _loaded = False
+
+    def __call__(self, *args, **params):
+        super().__call__(*args, **params)
+        if not self._loaded:
+            Store.output_settings.initialize(list(Store.renderers.keys()))
+            Store.set_display_hook('html+js', LabelledData, render_html)
+            Store.set_display_hook('png', LabelledData, render_png)
+            Store.set_display_hook('svg', LabelledData, render_svg)
+            pyodide_extension._loaded = True

holoviews/util/__init__.py

@@ -648,6 +648,8 @@ class extension(_pyviz_extension):
     # Hooks run when a backend is loaded
     _backend_hooks = defaultdict(list)
 
+    _loaded = False
+
     def __call__(self, *args, **params):
         # Get requested backends
         config = params.pop('config', {})