BUG: Base64-encode binary images in MIME bundle

get_mimebundle returned raw bytes for image/png, image/jpeg and
application/pdf. The jupyter messaging layer encodes these
automatically,
but consumers that read the MIME bundle directly do not. In particular,
quarto-live's pyodide engine builds a data URL straight from the value,
so plots failed to render in a {pyodide} cell.

Encode binary image data as base64 strings and decode svg to text so the
MIME bundle is valid for direct consumers as well as the jupyter kernel.

Author: has2k1

plotnine/_utils/ipython.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import base64
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
@@ -55,15 +56,22 @@ def get_mimebundle(
     }
     mimetype = lookup[format]
 
-    image: bytes | str = b
     metadata: dict[str, DisplayMetadata] = {}
     w, h = figure_size_px
     if format in ("png", "jpeg"):
         metadata = {mimetype: {"width": w, "height": h}}
     elif format == "retina":
         # `retina=True` in IPython.display.Image just halves width/height
         metadata = {mimetype: {"width": w // 2, "height": h // 2}}
-    elif format == "svg":
-        image = b.decode()
 
-    return {mimetype: image}, metadata
+    # The display data for a binary image must be base64 encoded and for
+    # svg it must be text. The jupyter messaging layer encodes the bytes
+    # automatically, but consumers that read the MIME bundle directly
+    # (e.g. quarto-live's pyodide engine) do not.
+    data: str = (
+        b.decode("utf-8")
+        if mimetype == "image/svg+xml"
+        else base64.b64encode(b).decode("ascii")
+    )
+
+    return {mimetype: data}, metadata

plotnine/typing.py

@@ -157,6 +157,4 @@ class DisplayMetadata(TypedDict):
     height: NotRequired[int]
 
 
-MimeBundle: TypeAlias = tuple[
-    dict[str, bytes | str], dict[str, DisplayMetadata]
-]
+MimeBundle: TypeAlias = tuple[dict[str, str], dict[str, DisplayMetadata]]