Restore output attribute of py-script tags, add py-script exec lifecycle hooks (#1063)

* Add beforePyScriptExec, afterPyScriptExec lifecycle hooks

* Add stdiodirector plugin for `output`, `stderr` attributes of py-script tag

* Add docs on `output` and `stderr` attributes of py-script tag

* Tests

* Removed output deprecation warning for `output` attribute

* Add createSingularWarning(), with createDeprecationWarning as alias

pyscriptjs/src/plugins/stdiodirector.ts

@@ -0,0 +1,53 @@
+import { Plugin } from "../plugin";
+import { TargetedStdio, StdioMultiplexer } from "../stdio";
+
+
+/**
+ * The StdioDirector plugin captures the output to Python's sys.stdio and
+ * sys.stderr and writes it to a specific element in the DOM. It does this by
+ * creating a new TargetedStdio manager and adding it to the global stdioMultiplexer's
+ * list of listeners prior to executing the Python in a specific tag. Following
+ * execution of the Python in that tag, it removes the TargetedStdio as a listener
+ *
+ */
+export class StdioDirector extends Plugin {
+    _stdioMultiplexer: StdioMultiplexer;
+
+    constructor(stdio: StdioMultiplexer) {
+        super()
+        this._stdioMultiplexer = stdio
+    }
+
+    /** Prior to a <py-script> tag being evaluated, if that tag itself has
+     * an 'output' attribute, a new TargetedStdio object is created and added
+     * to the stdioMultiplexer to route sys.stdout and sys.stdout to the DOM object
+     * with that ID for the duration of the evaluation.
+     *
+     */
+    beforePyScriptExec(runtime: any, src: any, PyScriptTag): void {
+        if (PyScriptTag.hasAttribute("output")){
+            const targeted_io = new TargetedStdio(PyScriptTag, "output", true, true)
+            PyScriptTag.stdout_manager = targeted_io
+            this._stdioMultiplexer.addListener(targeted_io)
+        }
+        if (PyScriptTag.hasAttribute("stderr")){
+            const targeted_io = new TargetedStdio(PyScriptTag, "stderr", false, true)
+            PyScriptTag.stderr_manager = targeted_io
+            this._stdioMultiplexer.addListener(targeted_io)
+        }
+    }
+
+    /** After a <py-script> tag is evaluated, if that tag has a 'stdout_manager'
+     *  (presumably TargetedStdio, or some other future IO handler), it is removed.
+     */
+    afterPyScriptExec(runtime: any, src: any, PyScriptTag: any, result: any): void {
+        if (PyScriptTag.stdout_manager != null){
+            this._stdioMultiplexer.removeListener(PyScriptTag.stdout_manager)
+            PyScriptTag.stdout_manager = null
+        }
+        if (PyScriptTag.stderr_manager != null){
+            this._stdioMultiplexer.removeListener(PyScriptTag.stderr_manager)
+            PyScriptTag.stderr_manager = null
+        }
+    }
+}