birdnotes.py: Objects to represent bird note files

This is a utility function used to attach the various child elements in the sighting-notes pattern.

# - - - S i g h t N o t e s . w r i t e C h i l d

    def writeChild(self, parent, childName, narr):
        """Attach a child and put narrative into it.
          [ (parent is an et.Element) and
            (childName is an element name as a string) and
            (narr is a Narrative instance or None) ->
              if  narr is not None ->
                parent  :=  parent with a new child named (childName)
                    attached, containing narr ]
              else -> I ]
        """
        #-- 1 --
        if  narr is None:
            return

        #-- 2 --
        # [ parent  :=  parent with a new childName child added
        #   child  :=  that new child ]
        child = et.SubElement(parent, childName)

See Section 18.6, “Narrative.writeNode(): Write as XML”.

        #-- 3 --
        # [ child  :=  child with narr added ]
        narr.writeNode(child)