python literals via pyodide

bin/resolve-dependencies

@@ -86,6 +86,10 @@ const mains = ["unpkg", "jsdelivr", "browser", "main"];
     const package = await resolve("leaflet");
     console.log(`export const leaflet = dependency("${package.name}", "${package.version}", "${package.export.replace(/-src\.js$/, ".js")}");`);
   }
+  {
+    const package = await resolve("pyodide");
+    console.log(`export const pyodide = "https://cdn.jsdelivr.net/pyodide/v${package.version}/full/pyodide.js";`);
+  }
 })();
 
 async function resolve(specifier) {

src/dependencies.js

@@ -19,3 +19,4 @@ export const topojson = dependency("topojson-client", "3.1.0", "dist/topojson-cl
 export const exceljs = dependency("exceljs", "4.3.0", "dist/exceljs.min.js");
 export const mermaid = dependency("mermaid", "9.1.1", "dist/mermaid.min.js");
 export const leaflet = dependency("leaflet", "1.8.0", "dist/leaflet.js");
+export const pyodide = "https://cdn.jsdelivr.net/pyodide/v0.20.0/full/pyodide.js";

src/library.js

@@ -10,6 +10,7 @@ import mermaid from "./mermaid.js";
 import Mutable from "./mutable.js";
 import now from "./now.js";
 import Promises from "./promises/index.js";
+import py from "./py.js";
 import resolve from "./resolve.js";
 import requirer, {requireDefault, setDefaultRequire} from "./require.js";
 import SQLite, {SQLiteDatabaseClient} from "./sqlite.js";
@@ -44,6 +45,7 @@ export default Object.assign(Object.defineProperties(function Library(resolver)
     Inputs: () => require(inputs.resolve()).then(Inputs => ({...Inputs, file: Inputs.fileOf(AbstractFile)})),
     L: () => leaflet(require),
     mermaid: () => mermaid(require),
+    py: () => py(require),
     Plot: () => require(plot.resolve()),
     require: () => require,
     resolve: () => resolve, // deprecated; use async require.resolve instead

src/py.js

@@ -0,0 +1,68 @@
+import {pyodide as Pyodide} from "./dependencies.js";
+
+export default async function py(require) {
+  const pyodide = await (await require(Pyodide)).loadPyodide();
+  let patch; // a promise for patching matplotlib (if needed)
+  return async function py(strings) {
+    const globals = {};
+    let code = strings[0];
+    for (let i = 1, n = arguments.length; i < n; ++i) {
+      const name = `_${i}`;
+      globals[name] = arguments[i];
+      code += name + strings[i];
+    }
+    const imports = findImports(pyodide, code);
+    if (imports.includes("matplotlib") && !patch) await (patch = patchMatplotlib(require, pyodide));
+    if (imports.length) await pyodide.loadPackagesFromImports(code);
+    const value = await pyodide.runPythonAsync(code, {globals: pyodide.toPy(globals)});
+    return pyodide.isPyProxy(value) ? value.toJs() : value;
+  };
+}
+
+// https://github.com/pyodide/pyodide/blob/1624e4a62445876a2d810fdbfc9ddb69a8321a8e/src/js/api.ts#L119-L125
+function findImports(pyodide, code) {
+  const imports = pyodide.pyodide_py.find_imports(code);
+  try {
+    return imports.toJs();
+  } finally {
+    imports.destroy();
+  }
+}
+
+// Overrides matplotlib’s show function to return a DIV such that when used as
+// the last expression in an Observable cell, the inspector will display it.
+async function patchMatplotlib(require, pyodide) {
+  require.resolve("[email protected]/css/font-awesome.min.css").then(href => {
+    const link = document.createElement("link");
+    link.rel = "stylesheet";
+    link.href = href;
+    document.head.appendChild(link);
+  });
+  await pyodide.loadPackage("matplotlib");
+  await pyodide.runPythonAsync(`from matplotlib import pyplot as plt
+from js import document
+
+_show = plt.show
+
+def create_root_element(self):
+  div = document.createElement("div")
+  document.body.appendChild(div)
+  return div
+
+def show(self):
+  f = plt.gcf()
+  c = f.canvas
+  c.create_root_element = create_root_element.__get__(c, c.__class__)
+  _show()
+  plt.close(f)
+  top = c.get_element("top")
+  if (top):
+    top.remove()
+  div = c.get_element("")
+  if (div.parentNode == document.body):
+    div.remove()
+  return div
+
+plt.show = show.__get__(plt, plt.__class__)
+`);
+}

test/index-test.js

@@ -34,6 +34,7 @@ test("new Library returns a library with the expected keys", async t => {
     "now",
     "olympians",
     "penguins",
+    "py",
     "require",
     "resolve",
     "svg",