code: def retrieve_GTF_field(field,gtf):
      
      inGTF=gtf.copy()
      def splits(x):
          l=x.split(";")
          l=[ s.split(" ") for s in l]
          res=np.nan
          for s in l:
              if field in s:
                  if '"' in s[-1]:
                      res=s[-1][1:-1]
                  else:
                      res=s[-1]
          return res
  
      inGTF[field]=inGTF['attribute'].apply(lambda x: splits(x))
      return inGTF[[field]]
docs: Returns a field of choice from the attribute column of the GTF
  
      :param field: field to be retrieved
      :returns: a Pandas dataframe with one columns containing the field of choice