code: def get_file_samples(file_ids):
      
      assert isinstance(file_ids, Iterable)
  
      # query TCGA API to get sample barcodes associated with file IDs
      payload = {
          "filters":json.dumps({
              "op":"in",
              "content":{
                  "field":"files.file_id",
                  "value": list(file_ids),
              }
          }),
          "fields":"file_id,cases.samples.submitter_id",
          "size":10000
      }
      r = requests.post('https://gdc-api.nci.nih.gov/files', data=payload)
      j = json.loads(r.content.decode('utf-8'))
      file_samples = OrderedDict()
      for hit in j['data']['hits']:
          file_id = hit['file_id']
          assert len(hit['cases']) == 1
          case = hit['cases'][0]
          assert len(case['samples']) == 1
          sample = case['samples'][0]
          sample_barcode = sample['submitter_id']
          file_samples[file_id] = sample_barcode
  
      df = pd.DataFrame.from_dict(file_samples, orient='index')
      df = df.reset_index()
      df.columns = ['file_id', 'sample_barcode']
      return df
docs: Get TCGA associated sample barcodes for a list of file IDs. 
      
      Params
      ------
      file_ids : Iterable
          The file IDs.
          
      Returns
      -------
      `pandas.Series`
          Series containing file IDs as index and corresponding sample barcodes.