Export array of objects each containing array of objects in a attribute in python

My data structure is like this:

Contents = [];
class Post:
  def __init__(self, poster,poster_url,post_text, post_images, post_comments):
    self.poster = poster
    self.poster_url = poster_url
    self.post_text = post_text
    self.post_images = post_images
    self.post_comments = post_comments    

class Comment:
  def __init__(self, poster,poster_url,post_text, post_images):
    self.poster = poster
    self.poster_url = poster_url
    self.post_text = post_text
    self.post_images = post_images 

I am trying to store array of comment inside post class and post class inside array Contents.But I am not finding any way to export this.How should I export this to formats like csv,excel or json?