Simple heuristics to determine python executable name across platforms (

#2247)

* Simple heuristics to determine python executable name across platforms.  Fixes #2181.

* Remove hardcoded reference to python3 in output to user.  Fix indentation problem.  Clarify some things in README files.

* Fixing linter issues

packages/aws-cdk/lib/init-templates/app/python/README.md → packages/aws-cdk/lib/init-templates/app/python/README.template.md

@@ -5,22 +5,17 @@ This is a blank project for Python development with CDK.
 
 The `cdk.json` file tells the CDK Toolkit how to execute your app.
 
-This project is set up like a standard Python project.  The initialization process also creates
-a virtualenv within this project, stored under the .env directory.  To create the virtualenv 
-it assumes that there is a `python3` executable in your path with access to the `venv` package.
-If for any reason the automatic creation of the virtualenv fails, you can create the virtualenv
-manually once the init process completes.
+This project is set up like a standard Python project.  The initialization
+process also creates a virtualenv within this project, stored under the .env
+directory.  To create the virtualenv it assumes that there is a `python3`
+(or `python` for Windows) executable in your path with access to the `venv`
+package. If for any reason the automatic creation of the virtualenv fails,
+you can create the virtualenv manually.
 
 To manually create a virtualenv on MacOS and Linux:
 
 ```
-$ python3 -m venv .env
-```
-
-For Windows, use:
-
-```
-% python -m venv .env
+$ %python-executable% -m venv .env
 ```
 
 After the init process completes and the virtualenv is created, you can use the following
@@ -48,8 +43,8 @@ At this point you can now synthesize the CloudFormation template for this code.
 $ cdk synth
 ```
 
-To add additional dependencies, for example other CDK libraries, just add to
-your requirements.txt file and rerun the `pip install -r requirements.txt`
+To add additional dependencies, for example other CDK libraries, just add
+them to your `setup.py` file and rerun the `pip install -r requirements.txt`
 command.
 
 # Useful commands

packages/aws-cdk/lib/init-templates/app/python/cdk.template.json

@@ -0,0 +1,3 @@
+{
+    "app": "%python-executable% app.py"
+}

packages/aws-cdk/lib/init-templates/sample-app/python/README.md → packages/aws-cdk/lib/init-templates/sample-app/python/README.template.md

@@ -15,13 +15,7 @@ manually once the init process completes.
 To manually create a virtualenv on MacOS and Linux:
 
 ```
-$ python3 -m venv .env
-```
-
-For Windows, use:
-
-```
-% python -m venv .env
+$ %python-executable% -m venv .env
 ```
 
 After the init process completes and the virtualenv is created, you can use the following

packages/aws-cdk/lib/init-templates/sample-app/python/cdk.template.json

@@ -0,0 +1,3 @@
+{
+    "app": "%python-executable% app.py"
+}

packages/aws-cdk/lib/init.ts

@@ -42,6 +42,16 @@ export async function cliInit(type?: string, language?: string, canUseNetwork?:
   await initializeProject(template, language, canUseNetwork !== undefined ? canUseNetwork : true);
 }
 
+/**
+ * Returns the name of the Python executable for this OS
+ */
+function pythonExecutable() {
+  let python = 'python3';
+  if (process.platform === 'win32') {
+    python = 'python';
+  }
+  return python;
+}
 const INFO_DOT_JSON = 'info.json';
 
 export class InitTemplate {
@@ -143,7 +153,8 @@ export class InitTemplate {
              .replace(/%name\.PascalCased%/g, camelCase(project.name, { pascalCase: true }))
              .replace(/%cdk-version%/g, cdkVersion)
              .replace(/%cdk-home%/g, CDK_HOME)
-             .replace(/%name\.PythonModule%/g, project.name.replace(/-/g, '_'));
+             .replace(/%name\.PythonModule%/g, project.name.replace(/-/g, '_'))
+             .replace(/%python-executable%/g, pythonExecutable());
   }
 }
 
@@ -233,7 +244,7 @@ async function postInstall(language: string, canUseNetwork: boolean) {
   case 'java':
     return await postInstallJava(canUseNetwork);
   case 'python':
-    return await postInstallPython(canUseNetwork);
+    return await postInstallPython();
   }
 }
 
@@ -263,17 +274,14 @@ async function postInstallJava(canUseNetwork: boolean) {
   await execute('mvn', 'package');
 }
 
-async function postInstallPython(canUseNetwork: boolean) {
-  if (!canUseNetwork) {
-    print(`Please run ${colors.green('python -m venv .env')}!`);
-    return;
-  }
-
-  print(`Executing ${colors.green('python -m venv .env')}`);
+async function postInstallPython() {
+  const python = pythonExecutable();
+  print(`Executing ${colors.green('Creating virtualenv...')}`);
   try {
-    await execute('python3', '-m venv', '.env');
+    await execute(python, '-m venv', '.env');
   } catch (e) {
-    throw new Error(`${colors.green('python3 -m venv .env')} failed: ` + e.message);
+    print('Unable to create virtualenv automatically');
+    print(`Please run ${colors.green(python + ' -m venv .env')}!`);
   }
 }