code: def ext():
      return ".xlsx"
  
imports: import contextlib
  from pathlib import Path
  import re
  import numpy
  import pytest
  import pandas
  from pandas import DataFrame
  import pandas._testing
  from pandas.io.excel import ExcelWriter, _OpenpyxlWriter
  from pandas.io.excel._openpyxl import OpenpyxlReader
label_desc: Use image node_id 1 for calling a global function with example usage: ext() and returns: str