code: def _item_exists_in_bucket(self, bucket, key, checksums):
          
          try:
              obj = self.target_s3.meta.client.head_object(Bucket=bucket, Key=key)
              if obj and obj.containsKey('Metadata'):
                  if obj['Metadata'] == checksums:
                      return True
          except ClientError:
              # An exception from calling `head_object` indicates that no file with the specified name could be found
              # in the specified bucket.
              return False
docs: Returns true if the key already exists in the current bucket and the clientside checksum matches the
          file's checksums, and false otherwise.