More questions on Python strings

[Dennis E. Evans]

  Hi 

I have a function that reads some meta data from a database and builds a default order by and where clause for a table.  

some details,  

  rows is a list of pyOdbc.Row and will look like this
  [1, 'ColumnName', 3, 5]
there will be one to n elements 

EmptyString, defaultColumn, defaultColumnParaMarker,
KeyLabelPos and a couple others are all constants stings or intergers defined in another module.
 

this is the function :

  def ReadPkColumns(self) :

    # fetch all the rows, this is the second result set in the call
    # this will be a very small result set, typically a PK will have 1,2 or 3 columns
    # on rare occasions a PK can have 4 or more
    rows = self.cursor.fetchall()
    
    # if there are no rows just assign an empty string
    # this is probably an error in the db
    if (len(rows) <= 0) :
      self.PkOrderBy = EmptyString
      self.PkWhereClause = EmptyString
    elif (len(rows) == 1) :
    # if there is one column then assign it no loops 
      self.PkOrderBy = defaultColumn.format(Ali=self.alias, ColLabel = rows[0][KeyLabelPos])
      self.PkWhereClause = defaultColumnParaMarker.format(Ali=self.alias, ColLabel = rows[0][KeyLabelPos])
    else :
      # two or more columns build a list of strings formatted 
      # as needed for the order by and where clause

      # create an empty list
      cols = []
      # add the formatted columns to the list
      for oneRow in rows :
        cols.append(defaultColumn.format(Ali=self.alias, ColLabel = oneRow[KeyLabelPos]))
      # and build the order by clause form the formatted strings
      self.PkOrderBy = CommaSpace.join(cols)
      
      # clear the cols list and fill again for use with the where clause 
      cols.clear()
      for oneRow in rows :
        cols.append(defaultColumnParaMarker.format(Ali=self.alias, ColLabel = oneRow[KeyLabelPos]))
      self.PkWhereClause = andConjunction.join(cols)
            
    return
# ------------------------------------------------------------------------------

 
my question is about this block
      # create an empty list
      cols = []
      # add the formatted columns to the list
      for oneRow in rows :
        cols.append(defaultColumn.format(Ali=self.alias, ColLabel = oneRow[KeyLabelPos]))
      # and build the order by clause form the formatted strings
      self.PkOrderBy = CommaSpace.join(cols)
      
      # clear the cols list and fill again for use with the where clause 
      cols.clear()
 
  I create an empty list and then fill it with some formatted strings and then assign to the order by instance member, clear the list and repeat for the where clause member.

  I tried a different things using the join statement and the rows instance to avoid the need to create the list of string (cols) but that resulted in various syntax and run time errors. 

  Is the a way to build the strings with out using the intermediate list? 

  the end result needs to look like this,

  self.OrderBy = "tableAlias.ColumnOne, tableAlias.ColumnTwo, ..."

  self.WhereClause = "(tableAlias.ColumnOne = ?) and (tableAlias.ColumnTwo = ?) and ..."

  thanks Dennis