text: import numpy as np
  import pandas as pd
  
  df = pd.DataFrame([[0 , 0.54543]], columns = ['date' , 'signal'])
  # all dates are int64 , min is also int64 and max is int64
  df['date'] = df['date'].astype(np.int64)
  df.info()
  print("min_max_date" , pd.Series([df['date'].min()]).dtype,
        pd.Series([df['date'].max()]).dtype)
  
  # all dates are int64 , min is also int64 and max is int64
  df['date'] = df['date'].astype(np.int32)
  df.info()
  print("min_max_date" , pd.Series([df['date'].min()]).dtype,
        pd.Series([df['date'].max()]).dtype)
  
  # now use, pandas series
  