docstr: Lookup a *name* in the table.
  
  Returns a *Symbol* instance.
code: def lookup(self, name):
      """Lookup a *name* in the table.
  
      Returns a *Symbol* instance.
      """
      sym = self._symbols.get(name)
      if sym is None:
          flags = self._table.symbols[name]
          namespaces = self.__check_children(name)
          module_scope = self._table.name == "top"
          sym = self._symbols[name] = Symbol(
              name, flags, namespaces, module_scope=module_scope
          )
      return sym
  
imports: import _symtable
  from _symtable import USE, DEF_GLOBAL, DEF_NONLOCAL, DEF_LOCAL, DEF_PARAM, DEF_IMPORT, DEF_BOUND, DEF_ANNOT, SCOPE_OFF, SCOPE_MASK, FREE, LOCAL, GLOBAL_IMPLICIT, GLOBAL_EXPLICIT, CELL
  import weakref
label_desc: Use image node_id 11 for calling the SymbolTable obj's underlying member method code with example usage: obj.lookup(name) and returns: sym