Python Lambda function using boto3 uploads 0 bytes image file to s3

Question

My use case is that I'm trying to take a screenshot of a view in Tableau, and save that screenshot in a bucket in s3. This is done through a Lambda function written in Python. The Lambda is assigned full access rights to s3 and is connected to the Internet.

Everything essentially works - there's no issues with access rights to s3, a connection to the Tableau account can be established, and a file is uploaded to s3. There's no errors thrown when the code is tested. There's one issue though: the saved file is an empty 0 bytes file.

Here's the code:

import logging
import traceback
import os
import requests
from datetime import datetime, timezone
import pytz
import json
from dotenv import load_dotenv
import tableauserverclient as TSC
from slack.web.client import WebClient
from slack.errors import SlackApiError
import boto3
import nest_asyncio
nest_asyncio.apply()

def lambda_handler(event,context):

    def Tableau2Slack():
        
        try:
            #Tableau environemnt variables
            tabAccount=os.environ['tabAccount'],
            tabPass=os.environ['tabPass'],
            tabDomain=os.environ['tabDomain'],
            tabServer=os.environ['tabServer'],
            tabView1=os.environ['tabView1'],
            tabPath1=os.environ['tabPath1']

            s3 = boto3.client('s3')
            bucket=os.environ['bucket']
            
        
            #Let's connect to Tableau
            print("Talking to Tableau...\n")
            tableau_auth = TSC.TableauAuth(tabAccount, tabPass, tabDomain)
            server = TSC.Server(tabServer)

            # Searching Tableau Online account for View1
            with server.auth.sign_in(tableau_auth):
                server.use_server_version()
                req_option = TSC.RequestOptions()
                req_option.filter.add(TSC.Filter(TSC.RequestOptions.Field.Name,
                                                 TSC.RequestOptions.Operator.Equals, tabView1))
                all_views, pagination_item = server.views.get(req_option)

                # Error catching for bad View names
                if not all_views:
                    raise LookupError("View with the specified name was not found.")
                view_item = all_views[0]

                image_req_option = TSC.ImageRequestOptions(imageresolution=TSC.ImageRequestOptions.Resolution.High,maxage=1)
                server.views.populate_image(view_item, image_req_option)
                print("Image saved in temporary folder...\n")

                date = datetime.utcnow().strftime('%Y_%m_%d')

                # Save bytes as image
                with open('/tmp' + tabPath1, "wb") as image_file1:
                    s3.upload_file('/tmp' + tabPath1, bucket, date + '_' + tabPath1)
                print("Tableau image successfully saved to s3 as {0}".format(tabPath1), '\n')

        # Tableau try statement error handling
        except:
            traceback.print_exc()

    Tableau2Slack()
    
    return print('Success!')

I suspect that there's something wrong where the file is opened and then uploaded to s3, but can't figure out what.

Running the same code locally, but instead of...

                with open('/tmp/' + tabPath1, "wb") as image_file1:
                    s3.upload_file('/tmp/' + tabPath1, bucket, date + '_' + tabPath1)

...replacing it with...

            with open(tabPath1, "wb") as image_file1:
                image_file1.write(view_item.image)

...saves a proper file of about 250 kb.

Any idea what could be going on? I'm out of ideas...