allow custom python binary. closes #48

README.md

@@ -108,6 +108,16 @@ custom:
     fileName: requirements-prod.txt
 ```
 
+## Customize Python executable
+Sometimes your Python executable isn't available on your `$PATH` as `python2.7`
+or `python3.6` (for example, windows or using pyenv).
+To support this, this plugin has the following option:
+```yaml
+custom:
+  pythonRequirements:
+    pythonBin: /opt/python3.6/bin/python
+```
+
 ## Manual invocations
 
 The `.requirements` and `requirements.zip`(if using zip support) files are left

index.js

@@ -53,21 +53,23 @@ class ServerlessPythonRequirements {
     }
 
     const runtime = this.serverless.service.provider.runtime;
+    const pythonBin = this.custom().pythonBin || runtime;
     this.serverless.cli.log(
       `Installing required Python packages for runtime ${runtime}...`);
 
     return new BbPromise((resolve, reject) => {
       let cmd;
       let options;
       const pipCmd = [
-        runtime, '-m', 'pip', '--isolated', 'install',
+        pythonBin, '-m', 'pip', '--isolated', 'install',
         '-t', '.requirements', '-r', fileName,
       ];
       if (this.custom().pipCmdExtraArgs) {
         pipCmd.push(...this.custom().pipCmdExtraArgs);
       }
       if (!this.custom().dockerizePip) {
-        const pipTestRes = spawnSync(runtime, ['-m', 'pip', 'help', 'install']);
+        const pipTestRes = spawnSync(
+          pythonBin, ['-m', 'pip', 'help', 'install']);
         if (pipTestRes.stdout.toString().indexOf('--system') >= 0)
           pipCmd.push('--system');
       }