Redid function as a decorator.

Provided example code.
Updated documentation.

README.md

@@ -1,12 +1,13 @@
-# aws_lambda_python_error_emailer
+# sns_error_notification
 
 ## Source
 The latest version of this code can be found at
-https://github.com/fdamstra/aws_lambda_python_error_emailer
+https://github.com/fdamstra/sns_error_notification
 
 ## Description
-This is a simple template you can add to your existing AWS Lambda python code
-so that it will email you details on your exceptions and errors.
+This is a simple python decorate for the aws serverless (lambda) 
+functions to make it easy to add email notification (or other SNS
+handling) for errors and exceptions.
 
 You can use CloudWatch to alert on errors, but then you just know that
 something went wrong, not _what_ went wrong. 
@@ -46,7 +47,10 @@ second.
 ## Set Up
 1. Configure an SNS topic.
 2. Subscribe to the SNS topic using your email address.
-3. Verify your subscription.
-4. Rename your `lambda_handler` function.
-5. Add the code from `lambda_function.py` to your function and make it the new handler.
+3. Grant your lanbda function `sns:Publish` permission.
+4. Set the environment variable `sns_error_topic` to your SNS topic's arn.
+5. Add `from sns_error_notification import sns_error_notification` to your handler.
+6. Add the line `@sns_error_notification` directly before your handler function.
+
+See the example.py for an example.
 

example.py

@@ -0,0 +1,14 @@
+#! /usr/bin/env python3
+from sns_error_notification import sns_error_notification
+
+def myfunc(a):
+    # Myfunc generates an exception
+    print(a[1])
+    return True
+
+@sns_error_notification
+def lambda_handler(event, context):
+    # Our lambda handler doesn't have any error.
+    myfunc(123)
+    return True
+

lambda_function.py

@@ -1,40 +0,0 @@
-#! /usr/bin/env python3
-import boto3
-import json
-import traceback
-
-# Insert original code here:
-
-# Rename your original lambda_handler() to lambda_handler_noemail()
-def lambda_handler_noemail(event, context):
-    # if you start generating too many emails, you can always change
-    # the handler back to this.
-    return True
-
-# Make this your caller.
-def lambda_handler(event, context):
-    # Set this to an SNS topic you'd like to publish to.
-    sns_arn = 'arn:aws:sns:us-east-2:1234567890:lambda-errors',
-    try:
-        snsclient = boto3.client('sns')
-        return lambda_handler_unhandled(event, context)
-    except Exception as e:
-        subject = f'Execution Error in {context.function_name}'
-        estr = str(e)
-        tb = traceback.format_exc()
-        try:
-            event_dump = json.dumps(event, indent=2)
-        except:
-            event_dump = "ERROR"
-        try: 
-            context_dump = vars(context)
-        except:
-            context_dump = "ERROR"
-        message = f'Exception: {estr}\n\nTraceback: {tb}\n\nEvent: {event_dump}\n\nContext: {context_dump}\n'
-        # Only happens if there was an exception
-        snsclient.publish(
-            Subject=subject,
-            TopicArn=sns_arn,
-            Message=message
-        )
-        raise

sns_error_notification.py

@@ -0,0 +1,56 @@
+#! /usr/bin/env python3
+''' sns_error_notification is intended as a wrapper around the `lambda_handler()`
+    function in an AWS serverless design. It catches errors and exceptions and
+    posts them to an sns queue, which can then be subscribed to for emails or
+    handled by another lambda function. 
+
+    To use:
+      1) Set the environment variable 'sns_error_topic' in your lambda
+         function to the arn of an SNS topic.
+      2) Ensure your lambda function has permission for `sns:Publish` to
+         the sns topic.
+      3) Import this function via 
+         `from sns_error_notification import sns_error_nofication`
+      4) Add `@sns_error_notification` directly before your lambda_handler
+         definition (`def lambda_handler(event, context):`)
+
+    WARNING: Could potentially generate a lot of email traffic on a high
+             volume function. Watch your execution errors metric in 
+             CloudWatch before deploying.
+
+    See https://github.com/fdamstra/sns_error_notification
+'''
+import boto3
+import json
+import os
+import traceback
+
+def sns_error_notification(function_name):
+    def wrapper(event, context):
+        try:
+            sns_arn = os.environ.get('sns_error_topic',
+              'Please set an environment variable "sns_error" topic')            
+            snsclient = boto3.client('sns')
+            function_name(event, context)
+        except Exception as e:
+            # First level error handling, send full details
+            subject = f'Execution Error in {context.function_name}'
+            estr = str(e)
+            tb = traceback.format_exc()
+            try:
+                event_dump = json.dumps(event, indent=2)
+            except:
+                event_dump = "ERROR"
+            try:
+                context_dump = vars(context)
+            except:
+                context_dump = "ERROR"
+            message = f'Exception:\n{estr}\n\nTraceback:\n{tb}\n\nEvent:\n{event_dump}\n\nContext:\n{context_dump}\n'
+            # Only happens if there was an exception
+            snsclient.publish(
+                TopicArn='arn:aws:sns:us-east-2:082012130604:lambda-errors',
+                Subject=subject,
+                Message=message
+            )
+            raise
+    return wrapper