Python serializable objects json

Question

class gpagelet:
    """
    Holds   1) the pagelet xpath, which is a string
            2) the list of pagelet shingles, list
    """
    def __init__(self, parent):
        if not isinstance( parent, gwebpage):
            raise Exception("Parent must be an instance of gwebpage")
        self.parent = parent    # This must be a gwebpage instance
        self.xpath = None       # String
        self.visibleShingles = [] # list of tuples
        self.invisibleShingles = [] # list of tuples
        self.urls = [] # list of string

class gwebpage:
    """
    Holds all the datastructure after the results have been parsed
    holds:  1) lists of gpagelets
            2) loc, string, location of the file that represents it
    """
    def __init__(self, url):
        self.url = url              # Str
        self.netloc = False         # Str
        self.gpagelets = []         # gpagelets instance
        self.page_key = ""          # str

Is there a way for me to make my class json serializable? The thing that I am worried is the recursive reference.

Answer 1

Indirect answer: instead of using JSON, you could use YAML, which has no problem doing what you want. (JSON is essentially a subset of YAML.)

Example:

import yaml
o1 = gwebpage("url")
o2 = gpagelet(o1)
o1.gpagelets = [o2]
print yaml.dump(o1)

In fact, YAML nicely handles cyclic references for you.

Answer 2

you can write your own encode and decoder, which can be very simple like return __dict__

e.g. here is a encoder to dump totally recursive tree structure, you can enhance it or use as it is for your own purpose

import simplejson

class Tree(object):
    def __init__(self, name, childTrees=None):
        self.name = name
        if childTrees is None:
            childTrees = []
        self.childTrees = childTrees

def encode_tree(obj):
    if not isinstance(obj, Tree):
        raise TypeError("%r is not JSON serializable" % (o,))

    return obj.__dict__

c1 = Tree("c1")
c2 = Tree("c2") 
t = Tree("t",[c1,c2])

print  simplejson.dumps(t, default=encode_tree)

it prints

{"childTrees": [{"childTrees": [], "name": "c1"}, {"childTrees": [], "name": "c2"}], "name": "t"}

you can similarly write a decoder but there you will somehow need to identify is it is your object or not, so may be you can put a type too if needed.