Ensure not clobbering same file. Fixes #1842 (#1843)

* Ensure not clobbering same file. Fixes #1842

* Remove command file after execution

Author: brollb

src/visualizers/widgets/TensorPlotter/TensorPlotterWidget.js

@@ -30,6 +30,7 @@ define([
         constructor(logger, container) {
             super(container);
             this._logger = logger.fork('Widget');
+            this.cmdCount = 0;
             this.currentPlotData = null;
 
             this.session = null;
@@ -95,8 +96,10 @@ define([
 
         async execPy(code) {
             try {
-                await this.session.addFile('last_cmd.py', code);
-                const {stdout} = await this.session.exec('python last_cmd.py');
+                const i = ++this.cmdCount;
+                await this.session.addFile(`cmd_${i}.py`, code);
+                const {stdout} = await this.session.exec(`python cmd_${i}.py`);
+                await this.session.removeFile(`cmd_${i}.py`);
                 return stdout;
             } catch (err) {
                 const {stderr} = err.jobResult;