[lxml] reconstruct a dtd content model

March 19, 2022

      I wonder if anybody has code to reconstruct the content definition of a DTD element. It's needed for some automatic 
documentation process.

I inherited a recursive code, but it's clear that it's doing the wrong thing; it's fairly obvious that the parentheses 
are being done wrongly. I think that parens ought to go before the occur processing at
"if node.occur == 'plus':", but it's also obvious that they are not always required.
...
content reconstruction test
'<!ELEMENT a (b?)>' content=( b ?)
'<!ELEMENT a (a|b)+>' content=( a  |  b +)
'<!ELEMENT a (a|b|c)+>' content=( a  |  b  |  c +)
'<!ELEMENT a (a|b?|c)+>' content=( a  |  b  |  c *)
'<!ELEMENT a (z)>' content=( z )
'<!ELEMENT a (#PCDATA)>' content=(#PCDATA)
'<!ELEMENT a (#PCDATA|b)*>' content=(#PCDATA |  b *)
'<!ELEMENT a (a,b,c)*>' content=( a  ,  b  ,  c *)
'<!ELEMENT a ANY>' content=ANY
'<!ELEMENT a EMPTY>' content=EMPTY
The code I have is as follows

def elementContent(node):
     return node.name

def _contentRecur(node, elFmt=elementContent):
     """
     node.type: ("element" | "seq")
     node.occur: ("once" | "opt")
     none.name: (str | None)
     """
     s = ""
     if node is  None:
         return s
     t = node.type
     left = node.left
     right = node.right
     if t == 'or':
         if left and right:
             s = f"{_contentRecur(left,elFmt=elFmt)} | {_contentRecur(right,elFmt=elFmt)}"
         elif left is not None:
             s = _contentRecur(left,elFmt=elFmt)
         elif right is not None:
             s = _contentRecur(right,elFmt=elFmt)
     elif t == 'seq':
         if left and right:
             s = f"{_contentRecur(left,elFmt=elFmt)} , {_contentRecur(right,elFmt=elFmt)}"
         elif left is not None:
             s = _contentRecur(left,elFmt=elFmt)
         elif right is not None:
             s = _contentRecur(right,elFmt=elFmt)
     elif t == "element":
         s = f" {elFmt(node)} "
     elif t=='pcdata':
         s = '#PCDATA'
     if node.occur == 'plus':
         s += "+"
     elif node.occur == 'opt':
         s += '?'
     elif node.occur=='mult':
         s += '*'
     return s

--
Robin Becker