Port of Wesley Chun's 'Using the Google Slides API with Python' to Google Apps Script. Read more at https://mashe.hawksey.info/?p=17385

slide_template.gs

// Port of Slides API demo by Wesley Chun to Google Apps Script
// Source: http://wescpy.blogspot.co.uk/2016/11/using-google-slides-api-with-python.html

function slides_template() {
  /*
  from apiclient import discovery
  from httplib2 import Http
  from oauth2client import file, client, tools
  */
  
  /* DIFF
  No comand line imports but some setup required. 
  1. Resources > Advance Services and enable the Slides API
     [Also change the identifier in the Libraries dialog to SLIDES to make it easy to compare to Wesley's code
  2. Resources > Developer Console Project click on the project link and enable Slides API 
  */

  var IMG_FILE = 'logo_slides_128px.png'      // use your own or copy https://goo.gl/hJwcoa !
  var TMPLFILE = 'Google Slides API template DEMO'   // use your own or use https://goo.gl/FdQ9AH !
  
  /*
  SCOPES = (
        'https://www.googleapis.com/auth/drive',
        'https://www.googleapis.com/auth/presentations',
    )
    store = file.Storage('storage.json')
    creds = store.get()
    if not creds or creds.invalid:
        flow = client.flow_from_clientsecrets('client_secret.json', SCOPES)
        creds = tools.run_flow(flow, store)
    HTTP = creds.authorize(Http())
    DRIVE  = discovery.build('drive',  'v3', http=HTTP)
    SLIDES = discovery.build('slides', 'v1', http=HTTP)
  */
  
  /* DIFF
  Tip by Romain Vialard that if you use DriveApp you can use the project token
  Running the function also automatically triggers any authorization required
  https://plus.google.com/u/0/+MartinHawksey/posts/aPEdvRiFV9Y
  */
  // SLIDES.setTokenService(function(){return ScriptApp.getOAuthToken()});
  
  /*
  rsp = DRIVE.files().list(q="name='%s'" % TMPLFILE).execute().get('files')[0]
  DATA = {'name': 'Google Slides API template DEMO'}
  print('** Copying template %r as %r' % (rsp['name'], DATA['name']))
  DECK_ID = DRIVE.files().copy(body=DATA, fileId=rsp['id']).execute().get('id')
  */
  
  /* DIFF
  As Google Apps Script has built-in DriveApp service we can use this to get out template 
  and copy it
  */
  Logger.log('** Copying template **');
  var DECK_ID = DriveApp.getFilesByName(TMPLFILE).next().makeCopy().getId();
  
  /*
  print('** Get slide objects, search for image placeholder')
  slide = SLIDES.presentations().get(presentationId=DECK_ID,
          fields='slides').execute().get('slides')[0]
  obj = None
  for obj in slide['pageElements']:
      if obj['shape']['shapeType'] == 'RECTANGLE':
          break
  */
  
  /* DIFF
  None really other than a slighlty difference call and port from py to js
  */
  Logger.log('** Get slide objects, search for image placeholder');
  
  // var slide = SLIDES.presentationsGet(DECK_ID).slides[0];
  var slide = SLIDES.Presentations.get(DECK_ID).slides[0];
  var obj
  for (var i in slide['pageElements']){
    var obj = slide['pageElements'][i];
    if (obj['shape']['shapeType'] == 'RECTANGLE'){
      break;
    }
  }

  /*
  print('** Searching for icon file')
  rsp = DRIVE.files().list(q="name='%s'" % IMG_FILE).execute().get('files')[0]
  print(' - Found image %r' % rsp['name'])
  img_url = '%s&access_token=%s' % (
          DRIVE.files().get_media(fileId=rsp['id']).uri, creds.access_token)
  */
  
  /* DIFF
  Using built-in DriveApp. The 'https://drive.google.com/uc?id=XXX' tip 
  thanks to Romain Vialard https://plus.google.com/+MartinHawksey/posts/aaMshWDR1PZ 
  */
  Logger.log('** Searching for icon file');
  var rsp = DriveApp.getFilesByName(IMG_FILE).next();
  Logger.log(Utilities.formatString(' - Found image %s', rsp.getId()));
  // var img_url = 'https://drive.google.com/uc?id='+rsp.getId(); // requires share access
  var img_url = rsp.getDownloadUrl()+"&access_token="+ScriptApp.getOAuthToken();
  
  /*
  print('** Replacing placeholder text and icon')
  reqs = [
      {'replaceAllText': {
          'containsText': {'text': '{{NAME}}'},
          'replaceText': 'Hello World!'
      }},
      {'createImage': {
          'url': img_url,
          'elementProperties': {
              'pageObjectId': slide['objectId'],
              'size': obj['size'],
              'transform': obj['transform'],
          }
      }},
      {'deleteObject': {'objectId': obj['objectId']}},
  ]
  */
  
  /* DIFF
  None other than Logger
  */
  Logger.log('** Replacing placeholder text and icon');
  var reqs = [
      {'replaceAllText': {
          'containsText': {'text': '{{NAME}}'},
          'replaceText': 'Hello World!'
      }},
      {'createImage': {
          'url': img_url,
          'elementProperties': {
              'pageObjectId': slide['objectId'],
              'size': obj['size'],
              'transform': obj['transform'],
          }
      }},
      {'deleteObject': {'objectId': obj['objectId']}},
  ];
  
  /*
  SLIDES.presentations().batchUpdate(body={'requests': reqs},
          presentationId=DECK_ID).execute()
  */
  
  /* DIFF
  Slightly different call presentationsBatchUpdate(presentationId,BatchUpdatePresentationRequestResource,options)
  */
  // SLIDES.presentationsBatchUpdate(DECK_ID, {'requests': reqs});
  SLIDES.Presentations.batchUpdate({'requests': reqs}, DECK_ID);

  Logger.log('DONE '); 
}

Thank you for this! I was having a hard time getting started on the slides API. I do have a question though. When I run this with my own slide template and photo it seems as though the photo ends up being skewed and smaller than the original shape. Is there a way to have it center crop the photo into the shape? I've been messing with the transform parameter a bit but don't seem to understand how it works.

Figured out I could use this instead

`var reqs = [

{"replaceAllShapesWithImage": {

"imageUrl": img_url,
"replaceMethod": "CENTER_CROP",
"containsText": {
"text": "Main_Image",
"matchCase": "True",
}
},},`

ReferenceError: "SLIDES" is not defined.
    at slides_template(Playground:95)

it should be written as "Slides" instead of "SLIDES", e.g.
SLIDES.Presentations.batchUpdate({'requests': reqs}, DECK_ID);
-> correct:
Slides.Presentations.batchUpdate({'requests': reqs}, DECK_ID);