Serialization based on ast.literal_eval

## Project description

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, 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.

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

# -*- coding: utf-8 -*-
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"))

print("Data:")
pprint.pprint(data)

# you can also use ast.literal_eval if you like
data2 = ast.literal_eval(ser_string)

assert data2==data


When you run this 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': '€'}


## Project details

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