input: Write a python function to extract tables from any Wikipedia page.
  assert extract_tables("https://en.wikipedia.org/wiki/List_of_countries_and_dependencies_by_population")[0] == ['Rank', 'Country(territory or dependency)', 'Population', 'Date', 'Percentage ofworldpopulation', 'Source']
  assert len(extract_tables("https://en.wikipedia.org/wiki/List_of_countries_and_dependencies_by_population")[1]) > 0
output: def extract_tables(url):
      import pandas as pd
      
      tables = pd.read_html(url)
      return [table.columns.tolist() for table in tables]