class_docstr: Expression base class
  
  Expression is designed to handle the calculation of data with the format below
  data with two dimension for each instrument,
  
  - feature
  - time:  it  could be observation time or period time.
  
      - period time is designed for Point-in-time database.  For example, the period time maybe 2014Q4, its value can observed for multiple times(different value may be observed at different time due to amendment).
class_docstr_tok: ["Expression","base","class","Expression","is","designed","to","handle","the","calculation","of","data","with","the","format","below","data","with","two","dimension","for","each","instrument",",","-","feature","-","time",":","it","could","be","observation","time","or","period","time",".","-","period","time","is","designed","for","Point-in-time","database",".","For","example",",","the","period","time","maybe","2014Q4",",","its","value","can","observed","for","multiple","times","(","different","value","may","be","observed","at","different","time","due","to","amendment",")","."]
docstr: get_extend_window_size
  
  For to calculate this Operator in range[start_index, end_index]
  We have to get the *leaf feature* in
  range[start_index - lft_etd, end_index + rght_etd].
  
  Returns
  ----------
  (int, int)
      lft_etd, rght_etd
docstr_tok: ["get_extend_window_size","For","to","calculate","this","Operator","in","range","[","start_index",",","end_index","]","We","have","to","get","the","*","leaf","feature","*","in","range","[","start_index","-","lft_etd",",","end_index","+","rght_etd","]",".","Returns","--","--","--","--","--","(","int",",","int",")","lft_etd",",","rght_etd"]
code: def get_extended_window_size(self):
      """get_extend_window_size
  
      For to calculate this Operator in range[start_index, end_index]
      We have to get the *leaf feature* in
      range[start_index - lft_etd, end_index + rght_etd].
  
      Returns
      ----------
      (int, int)
          lft_etd, rght_etd
      """
      raise NotImplementedError(
          "This function must be implemented in your newly defined feature"
      )
  
imports: from __future__ import division
  from __future__ import print_function
  import abc
  import pandas
  from ..log import get_module_logger
label_desc: Use image node_id 28 for calling the Expression obj's underlying member method code with example usage: obj.get_extended_window_size() without return types