serpent 1.18

Serialization based on ast.literal_eval

Serpent is a simple serialization library based on ast.literal_eval.

Because it only serializes literals and recreates the objects using ast.literal_eval(), the serialized data is safe to transport to other machines (over the network for instance) and de-serialize it there.

There is also a Java and a .NET (C#) implementation available. This allows for easy data transfer between the various ecosystems. You can get the full source distribution, a Java .jar file, and a .NET assembly dll. The java library can be obtained from Maven central (groupid net.razorvine artifactid serpent), and the .NET assembly can be obtained from Nuget.org (package Razorvine.Serpent).

API

• ser_bytes = serpent.dumps(obj, indent=False, set_literals=True, module_in_classname=False): # serialize obj tree to bytes

• obj = serpent.loads(ser_bytes) # deserialize bytes back into object tree

• You can use ast.literal_eval yourself to deserialize, but serpent.deserialize works around a few corner cases. See source for details.

Serpent is more sophisticated than a simple repr() + literal_eval():

• it serializes directly to bytes (utf-8 encoded), instead of a string, so it can immediately be saved to a file or sent over a socket

• it encodes byte-types as base-64 instead of inefficient escaping notation that repr would use (this does mean you have to base-64 decode these strings manually on the receiving side to get your bytes back. You can use the serpent.tobytes utility function for this.)

• it contains a few custom serializers for several additional Python types such as uuid, datetime, array and decimal

• it tries to serialize unrecognised types as a dict (you can control this with __getstate__ on your own types)

• it can create a pretty-printed (indented) output for readability purposes

• it outputs the keys of sets and dicts in alphabetical order (when pretty-printing)

• it works around a few quirks of ast.literal_eval() on the various Python implementations

Serpent allows comments in the serialized data (because it is just Python source code). Serpent can’t serialize object graphs (when an object refers to itself); it will then crash with a ValueError pointing out the problem.

Works with Python 2.7+ (including 3.x), IronPython 2.7+, Jython 2.7+.

FAQ

• Why not use XML? Answer: because XML.

• Why not use JSON? Answer: because JSON is quite limited in the number of datatypes it supports, and you can’t use comments in a JSON file.

• Why not use pickle? Answer: because pickle has security problems.

• Why not use repr()/ast.literal_eval()? See above; serpent is a superset of this and provides more convenience. Serpent provides automatic serialization mappings for types other than the builtin primitive types. repr() can’t serialize these to literals that ast.literal_eval() understands.

• Why not a binary format? Answer: because binary isn’t readable by humans.

• But I don’t care about readability. Answer: doesn’t matter, ast.literal_eval() wants a literal string, so that is what we produce.

• But I want better performance. Answer: ok, maybe you shouldn’t use serpent in this case. Find an efficient binary protocol (protobuf?)

• Why only Python, Java and C#/.NET, but no bindings for insert-favorite-language-here? Answer: I don’t speak that language. Maybe you could port serpent yourself?

• Where is the source? It’s on Github: https://github.com/irmen/Serpent

• Can I use it everywhere? Sure, as long as you keep the copyright and disclaimer somewhere. See the LICENSE file.

Demo

# This demo script is written for Python 3.2+
# -*- coding: utf-8 -*-
from __future__ import print_function
import ast
import uuid
import datetime
import pprint
import serpent


class DemoClass:
    def __init__(self):
        self.i=42
        self.b=False

data = {
    "names": ["Harry", "Sally", "Peter"],
    "big": 2**200,
    "colorset": { "red", "green" },
    "id": uuid.uuid4(),
    "timestamp": datetime.datetime.now(),
    "class": DemoClass(),
    "unicode": "€"
}

# serialize it
ser = serpent.dumps(data, indent=True)
open("data.serpent", "wb").write(ser)

print("Serialized form:")
print(ser.decode("utf-8"))

# read it back
data = serpent.load(open("data.serpent", "rb"))
print("Data:")
pprint.pprint(data)

# you can also use ast.literal_eval if you like
ser_string = open("data.serpent", "r", encoding="utf-8").read()
data2 = ast.literal_eval(ser_string)

assert data2==data

When you run this (with python 3.2+) it prints:

Serialized form:
# serpent utf-8 python3.2
{
  'big': 1606938044258990275541962092341162602522202993782792835301376,
  'class': {
    '__class__': 'DemoClass',
    'b': False,
    'i': 42
  },
  'colorset': {
    'green',
    'red'
  },
  'id': 'e461378a-201d-4844-8119-7c1570d9d186',
  'names': [
    'Harry',
    'Sally',
    'Peter'
  ],
  'timestamp': '2013-04-02T00:23:00.924000',
  'unicode': '€'
}
Data:
{'big': 1606938044258990275541962092341162602522202993782792835301376,
 'class': {'__class__': 'DemoClass', 'b': False, 'i': 42},
 'colorset': {'green', 'red'},
 'id': 'e461378a-201d-4844-8119-7c1570d9d186',
 'names': ['Harry', 'Sally', 'Peter'],
 'timestamp': '2013-04-02T00:23:00.924000',
 'unicode': '€'}