Allow clearing Pyodide text console with os.system("clear")

cypress/e2e/spec-wc-pyodide.cy.js

@@ -13,7 +13,8 @@ import {
   stopProject,
 } from "../helpers/editor.js";
 
-const origin = "http://localhost:3011/web-component.html";
+const origin =
+  Cypress.env("EDITOR_ORIGIN") || "http://localhost:3011/web-component.html";
 
 beforeEach(() => {
   cy.intercept("*", (req) => {
@@ -226,6 +227,20 @@ print(text_out)
     );
   });
 
+  it("clears the console when os.system('clear') is called", () => {
+    runCode('print("before")\nimport os\nos.system("clear")\nprint("after")');
+    getPythonConsoleOutput().should("contain", "after");
+    getPythonConsoleOutput().should("not.contain.text", "before");
+  });
+
+  it("clears buffered output written without a newline before clearing", () => {
+    runCode(
+      'import os\nprint("partial", end="")\nos.system("clear")\nprint("after")',
+    );
+    getPythonConsoleOutput().should("contain", "after");
+    getPythonConsoleOutput().should("not.contain.text", "partial");
+  });
+
   it("clears user-defined variables between code runs", () => {
     runCode("a = 1\nprint(a)");
     getPythonConsoleOutput().should("contain", "1");

src/PyodideWorker.js

@@ -410,6 +410,7 @@ const PyodideWorker = () => {
         postMessage({ method: "handleFileWrite", filename, content, mode });
       },
       locals: () => pyodide.runPython("globals()"),
+      clear_console: () => postMessage({ method: "handleClear" }),
     },
   };
 
@@ -443,6 +444,21 @@ const PyodideWorker = () => {
 
     pyodide.registerJsModule("basthon", fakeBasthonPackage);
 
+    await pyodide.runPythonAsync(`
+    import os as _os, sys as _sys, basthon as _basthon
+    _real_system = _os.system
+    def _patched_system(command):
+        if isinstance(command, str) and command.strip().lower() in ("clear", "cls"):
+            _sys.stdout.write("\\n")
+            _sys.stderr.write("\\n")
+            _sys.stdout.flush()
+            _sys.stderr.flush()
+            _basthon.kernel.clear_console()
+            return 0
+        return _real_system(command)
+    _os.system = _patched_system
+    `);
+
     await pyodide.runPythonAsync(`
     __old_input__ = input
     def __patched_input__(prompt=False):

src/components/Editor/Runners/PythonRunner/PyodideRunner/PyodideRunner.jsx

@@ -114,6 +114,9 @@ const PyodideRunner = ({
           case "handleOutput":
             handleOutput(data.stream, data.content);
             break;
+          case "handleClear":
+            clearConsole();
+            break;
           case "handleError":
             handleError(
               data.file,
@@ -210,6 +213,10 @@ const PyodideRunner = ({
     node.scrollTop = node.scrollHeight;
   };
 
+  const clearConsole = () => {
+    output.current.innerHTML = "";
+  };
+
   const handleError = (file, line, mistake, type, info) => {
     let errorMessage;
 
@@ -290,7 +297,7 @@ const PyodideRunner = ({
   };
 
   const handleRun = async () => {
-    output.current.innerHTML = "";
+    clearConsole();
     dispatch(setError(""));
     dispatch(setFriendlyError(null));
     setVisuals([]);

src/components/Editor/Runners/PythonRunner/PyodideRunner/PyodideRunner.test.js

@@ -260,6 +260,28 @@ describe("When output is received", () => {
   });
 });
 
+describe("When a clear console message is received", () => {
+  beforeEach(() => {
+    render(
+      <Provider store={store}>
+        <PyodideRunner active={true} />,
+      </Provider>,
+    );
+
+    const worker = PyodideWorker.getLastInstance();
+    worker.postMessageFromWorker({
+      method: "handleOutput",
+      stream: "stdout",
+      content: "hello",
+    });
+    worker.postMessageFromWorker({ method: "handleClear" });
+  });
+
+  test("it clears previously printed output", () => {
+    expect(screen.queryByText("hello")).not.toBeInTheDocument();
+  });
+});
+
 describe("When file write event is received", () => {
   let worker;
   beforeEach(() => {

src/components/Editor/Runners/PythonRunner/PyodideRunner/PyodideWorker.test.js

@@ -96,6 +96,29 @@ describe("PyodideWorker", () => {
     );
   });
 
+  test("it patches os.system to handle clear/cls", async () => {
+    expect(pyodide.runPythonAsync).toHaveBeenCalledWith(
+      expect.stringMatching(/os\.system/),
+    );
+  });
+
+  test("it forces batched output to flush before clearing", async () => {
+    expect(pyodide.runPythonAsync).toHaveBeenCalledWith(
+      expect.stringMatching(/_sys\.stdout\.write\("\\n"\)/),
+    );
+    expect(pyodide.runPythonAsync).toHaveBeenCalledWith(
+      expect.stringMatching(/_sys\.stderr\.write\("\\n"\)/),
+    );
+  });
+
+  test("the basthon clear_console bridge posts handleClear", () => {
+    const basthonCall = pyodide.registerJsModule.mock.calls.find(
+      ([name]) => name === "basthon",
+    );
+    basthonCall[1].kernel.clear_console();
+    expect(global.postMessage).toHaveBeenCalledWith({ method: "handleClear" });
+  });
+
   test("it patches urllib and requests modules", async () => {
     expect(pyodide.runPythonAsync).toHaveBeenCalledWith(
       expect.stringMatching(/pyodide_http.patch_all()/),