What is faster - Loading a pickled dictionary object or Loading a JSON file - to a dictionary?

Question

What is faster:

(A) 'Unpickling' (Loading) a pickled dictionary object, using pickle.load()

or

(B) Loading a JSON file to a dictionary using simplejson.load()

Assuming: The pickled object file exists already in case A, and that the JSON file exists already in case B.

Answer 1

The speed actually depends on the data, it's content and size.

But, anyway, let's take an example json data and see what is faster (Ubuntu 12.04, python 2.7.3) :

• pickle
• cPickle
• json
• simplejson
• ujson
• yajl

Giving this json structure dumped into test.json and test.pickle files:

{
    "glossary": {
        "title": "example glossary",
        "GlossDiv": {
            "title": "S",
            "GlossList": {
                "GlossEntry": {
                    "ID": "SGML",
                    "SortAs": "SGML",
                    "GlossTerm": "Standard Generalized Markup Language",
                    "Acronym": "SGML",
                    "Abbrev": "ISO 8879:1986",
                    "GlossDef": {
                        "para": "A meta-markup language, used to create markup languages such as DocBook.",
                        "GlossSeeAlso": ["GML", "XML"]
                    },
                    "GlossSee": "markup"
                }
            }
        }
    }
}

Testing script:

import timeit

import pickle
import cPickle

import json
import simplejson
import ujson
import yajl


def load_pickle(f):
    return pickle.load(f)


def load_cpickle(f):
    return cPickle.load(f)


def load_json(f):
    return json.load(f)


def load_simplejson(f):
    return simplejson.load(f)


def load_ujson(f):
    return ujson.load(f)


def load_yajl(f):
    return yajl.load(f)


print "pickle:"
print timeit.Timer('load_pickle(open("test.pickle"))', 'from __main__ import load_pickle').timeit()

print "cpickle:"
print timeit.Timer('load_cpickle(open("test.pickle"))', 'from __main__ import load_cpickle').timeit()

print "json:"
print timeit.Timer('load_json(open("test.json"))', 'from __main__ import load_json').timeit()

print "simplejson:"
print timeit.Timer('load_simplejson(open("test.json"))', 'from __main__ import load_simplejson').timeit()

print "ujson:"
print timeit.Timer('load_ujson(open("test.json"))', 'from __main__ import load_ujson').timeit()

print "yajl:"
print timeit.Timer('load_yajl(open("test.json"))', 'from __main__ import load_yajl').timeit()

Output:

pickle:
107.936687946

cpickle:
28.4231381416

json:
31.6450419426

simplejson:
20.5853149891

ujson:
16.9352178574

yajl:
18.9763481617

As you can see, unpickling via pickle is not that fast at all - cPickle is definetely the way to go if you choose pickling/unpickling option. ujson looks promising among these json parsers on this particular data.

Also, json and simplejson libraries load much faster on pypy (see Python JSON Performance).

See also:

• Python JSON decoding performance
• Pickle or json?
• Pickle vs JSON — Which is Faster?

It's important to note that the results may differ on your particular system, on other type and size of data.