code: def visit_variable(self, node, visited_children):
      question, name, cond_opt = visited_children
      cond = None
      if cond_opt:
          colon, cond = cond_opt[0]
      return types.tvariable(name, cond)
  
imports: from parsimonious import Grammar, NodeVisitor
  from hail.expr.nat import NatVariable
  from .None import types
  from hail.utils.java import unescape_parsable
label_desc: Use image node_id 3 for calling the TypeConstructor obj's underlying member method code with example usage: obj.visit_variable(node, visited_children) and returns: types