class_docstr: Yields the set of pure functions
code: def prepare(self, node):
      super(PureFunctions, self).prepare(node)
      self.result = {
          func
          for func, ae in self.argument_effects.items()
          if func not in self.global_effects and not any(ae)
      }
  
imports: from pythran.analyses.argument_effects import ArgumentEffects
  from pythran.analyses.global_effects import GlobalEffects
  from pythran.passmanager import ModuleAnalysis
label_desc: Use image node_id 2 for calling the PureFunctions obj's underlying member method code with example usage: obj.prepare(node) without return types