Merge pull request #329 from jacebrowning/cache-default-factory

Add caching to default factory calls

Author: jacebrowning

.verchew.ini

@@ -17,6 +17,6 @@ version = 1
 
 cli = dot
 cli_version_arg = -V
-version = 7 || 8 || 9 || 10
+version = graphviz
 optional = true
 message = This is only needed to generate UML diagrams for documentation.

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Release Notes
 
+## 2.2.3 (2024-05-26)
+
+- Added caching to default factory calls.
+
 ## 2.2.2 (2024-01-06)
 
 - Fixed `Manager.all()` behavior for patterns with default vales.

datafiles/utils.py

@@ -3,6 +3,7 @@
 import dataclasses
 import time
 from contextlib import suppress
+from dataclasses import Field
 from functools import lru_cache
 from pathlib import Path
 from pprint import pformat
@@ -30,14 +31,19 @@ def get_default_field_value(instance, name):
                 return field.default
 
             if not isinstance(field.default_factory, Missing):  # type: ignore
-                return field.default_factory()  # type: ignore
+                return _call_default_factory(field)
 
             if not field.init and hasattr(instance, "__post_init__"):
                 return getattr(instance, name)
 
     return Missing
 
 
+@cached
+def _call_default_factory(field: Field):
+    return field.default_factory()  # type: ignore
+
+
 def prettify(value) -> str:
     """Ensure value is a dictionary pretty-format it."""
     return pformat(dictify(value))

poetry.lock

@@ -1,7 +1,7 @@
 [tool.poetry]
 
 name = "datafiles"
-version = "2.2.2"
+version = "2.2.3"
 description = "File-based ORM for dataclasses."
 
 license = "MIT"

pyproject.toml

@@ -10,6 +10,8 @@
 
 from . import xfail_with_pep_563
 
+counter = 0
+
 
 @datafile("../tmp/sample.yml", manual=True)
 class SampleWithDefaults:
@@ -150,6 +152,27 @@ def when_file_exists(expect):
         expect(sample.b) == 3.4
         expect(sample.c) == 9.9
 
+    def it_only_calls_factory_when_needed(expect):
+        global counter
+        counter = 0
+
+        def default_factory():
+            global counter
+            counter += 1
+            logbreak(f"Called default factory: {counter}")
+            return "a"
+
+        @datafile("../tmp/sample.yml")
+        class Sample:
+            value: str = field(default_factory=default_factory)
+
+        sample = Sample()
+
+        sample.value = "b"
+        sample.value = "c"
+
+        expect(counter) == 2
+
 
 def describe_missing_attributes():
     @xfail_with_pep_563

tests/test_instantiation.py

@@ -46,7 +46,7 @@ def without_initial_values(sample, expect):
                 """
             )
 
-    def with_convertable_initial_values(expect):
+    def with_convertible_initial_values(expect):
         sample = Sample(1, 2, 3, 4)
 
         sample.datafile.save()