PersistentObjects 0.2.2

JSON-backed attribute-persistent object with namespace support

PersistentObjects

A simple Python library that provides the PersistentObject class, which automatically saves all its attributes to a JSON file. Attributes are saved as soon as they are set.

[!IMPORTANT] In-place mutations like .append(), .insert(), .extend(), etc. will not automatically save! Create a temp variable, mutate it, then reassign it back:

temp = pobject.my_list
temp.append("new item")
pobject.my_list = temp  # triggers save

Installation

pip install PersistentObjects

Usage

from PersistentObjects import PersistentObject

pobject = PersistentObject("save.json")

# attributes are saved to the json file immediately
pobject.first_value = 10
pobject.second_value = "foo"

# namespaces create sub-dicts in the json file
pobject.namespace("test_namespace")
pobject.test_namespace.third_value = [10, 5]

# or save the namespace to a variable
namespace = pobject.namespace("other_namespace")
namespace.value = 42

# suffix with '_' to make an attribute non-persistent (normal python attribute)
pobject.temp_ = True

# delete a persistent attribute
del pobject.first_value

Namespaces

Use namespace() to create a named section within the JSON file. After calling namespace(), you can access it via dot notation. Namespaces can be nested arbitrarily deep.

# create and access via dot notation
pobject.namespace("ui")
pobject.ui.theme = "dark"
pobject.ui.font_size = 14

# nested namespaces
pobject.namespace("ui").namespace("colors")
pobject.ui.colors.primary = "#ff0000"
pobject.ui.colors.accent = "#0000ff"

# or chain it
colors = pobject.namespace("ui").namespace("colors")
colors.primary = "#ff0000"

[!NOTE] You must call .namespace() at least once before using dot-access. This is by design — without it, accessing a nonexistent attribute like pobject.typo would silently create an empty namespace instead of raising an AttributeError.

Supported types

Beyond the standard JSON types (str, int, float, bool, list, dict, None), the following Python types are automatically encoded and decoded:

Type	JSON representation
tuple	{"__type__": "tuple", "__value__": [...]}
set	{"__type__": "set", "__value__": [...]}
frozenset	{"__type__": "frozenset", "__value__": [...]}
bytes	{"__type__": "bytes", "__value__": "<base64>"}
datetime	{"__type__": "datetime", "__value__": "<isoformat>"}
date	{"__type__": "date", "__value__": "<isoformat>"}
time	{"__type__": "time", "__value__": "<isoformat>"}

Nested structures work too (e.g. a list of tuples, a set of tuples).

from datetime import datetime

pobject.my_set = {1, 2, 3}
pobject.my_tuple = ("a", "b", "c")
pobject.my_bytes = b"hello"
pobject.my_datetime = datetime(2025, 6, 15, 12, 30)

Type enforcement

Use settype() to register a type constraint on an attribute. Assigning a value of the wrong type raises a TypeError.

from typing import Any

pobject.settype("count", int)
pobject.count = 5       # ok
pobject.count = "five"  # TypeError

# union types (Python 3.10+)
pobject.settype("value", int | None)
pobject.value = None    # ok

# tuple of types
pobject.settype("multi", (int, str))

# Any removes the constraint
pobject.settype("count", Any)

# also works on namespaces
namespace.settype("volume", int | float)

Defaults

Use setdefault() to set a value only if the attribute doesn't already exist. It also registers the value for reset(). An optional type parameter combines setting a default with type enforcement.

pobject.setdefault("name", "default_name")
pobject.setdefault("count", 0, type=int)  # sets default and enforces type

pobject.count = 99
pobject.reset("count")   # back to 0
pobject.reset()          # resets all attributes that have a registered default