"""This module provides some functions and classes to record and report
references to live object instances.
If you want live objects for a particular class to be tracked, you only have to
subclass from object_ref (instead of object).
About performance: This library has a minimal performance impact when enabled,
and no performance penalty at all when disabled (as object_ref becomes just an
alias to object in that case).
.. note:: PyPy uses a tracing garbage collector, so objects may
remain in the ``live_refs`` longer than expected, even after they
go out of scope. If deterministic behavior is required, you may need
to explicitly trigger garbage collection or call ``trackref.live_refs.clear()``.
"""
from __future__ import annotations
from collections import defaultdict
from operator import itemgetter
from time import monotonic_ns
from types import NoneType
from typing import TYPE_CHECKING, Any
from weakref import WeakKeyDictionary
if TYPE_CHECKING:
from collections.abc import Iterable
# typing.Self requires Python 3.11
from typing_extensions import Self
live_refs: defaultdict[type, WeakKeyDictionary] = defaultdict(WeakKeyDictionary)
[docs]
class object_ref:
"""Inherit from this class to a keep a record of live instances"""
__slots__ = ()
def __new__(cls, *args: Any, **kwargs: Any) -> Self:
obj = object.__new__(cls)
live_refs[cls][obj] = monotonic_ns()
return obj
# using Any as it's hard to type type(None)
def format_live_refs(ignore: Any = NoneType) -> str:
"""Return a tabular representation of tracked objects"""
s = "Live References\n\n"
now_ns = monotonic_ns()
for cls, wdict in sorted(live_refs.items(), key=lambda x: x[0].__name__):
if not wdict:
continue
if issubclass(cls, ignore):
continue
oldest_ns = min(wdict.values())
s += f"{cls.__name__:<30} {len(wdict):6} oldest: {int((now_ns - oldest_ns) // 1e9)}s ago\n"
return s
[docs]
def print_live_refs(*a: Any, **kw: Any) -> None:
"""Print tracked objects"""
print(format_live_refs(*a, **kw))
[docs]
def get_oldest(class_name: str) -> Any:
"""Get the oldest object for a specific class name"""
for cls, wdict in live_refs.items():
if cls.__name__ == class_name:
if not wdict:
break
return min(wdict.items(), key=itemgetter(1))[0]
return None
[docs]
def iter_all(class_name: str) -> Iterable[Any]:
"""Iterate over all objects of the same class by its class name"""
for cls, wdict in live_refs.items():
if cls.__name__ == class_name:
return wdict.keys()
return ()