Question

I have a function returning a dictionary:

 def to_dict(self):
     return dict({'identification': self.identifier,
                  'information': self.information,
                  'nodes': {e.position: e.to_dict for e in self.children}
                  })

Is there a way to optionally add each k/v? This does not work e.g:

def to_dict(self):
         return dict({'identification': self.identifier,
                      'information': self.information,
                      'nodes': {e.position: e.to_dict for e in self.children} if self.children
                      })

Is there a way to add in optional parts of dict creation without having to build a separate dictionary for each variation; is there a better way to do this even ?

Answer 1

Store the dict locally, update it with your extra info before returning:

def to_dict(self):
     retval = {'identification': self.identifier,
               'information': self.information,
              }
     if self.children:
         retval['nodes'] = {e.position: e.to_dict for e in self.children}
     return retval

I removed the dict() constructor in my example, it is entirely redundant. But because all your keys are also valid python identifiers, you could define your dict in a slightly more compact manner by using the dict() constructor and keyword arguments:

def to_dict(self):
     retval = dict(identification=self.identifier,
                   information=self.information)
     if self.children:
         retval['nodes'] = {e.position: e.to_dict for e in self.children}
     return retval