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gh-118761: Add helper to ensure that lazy imports are actually lazy by JelleZijlstra · Pull Request #132614 · python/cpython · GitHub

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gh-118761: Add helper to ensure that lazy imports are actually lazy #132614

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JelleZijlstra merged 2 commits into from
Apr 17, 2025
Conversation 8 Commits 2 Checks 0 Files changed
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gh-118761: Add helper to ensure that lazy imports are actually lazy #132614

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gh-118761: Add helper to ensure that lazy imports are actually lazy
JelleZijlstra Apr 16, 2025
a77577e
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JelleZijlstra Apr 17, 2025
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23 changes: 23 additions & 0 deletions Lib/test/support/import_helper.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
import os
import shutil
import sys
import textwrap
import unittest
import warnings

Expand Down Expand Up @@ -309,3 +310,25 @@ def ready_to_import(name=None, source=""):
sys.modules[name] = old_module
else:
sys.modules.pop(name, None)


def ensure_lazy_imports(imported_module, modules_to_block):
"""Test that when imported_module is imported, none of the modules in
modules_to_block are imported as a side effect."""
modules_to_block = frozenset(modules_to_block)
script = textwrap.dedent(
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f"""
import sys
modules_to_block = {modules_to_block}
if unexpected := modules_to_block & sys.modules.keys():
startup = ", ".join(unexpected)
raise AssertionError(f'unexpectedly imported at startup: {{startup}}')

import {imported_module}
if unexpected := modules_to_block & sys.modules.keys():
after = ", ".join(unexpected)
raise AssertionError(f'unexpectedly imported after importing {imported_module}: {{after}}')
"""
)
from .script_helper import assert_python_ok
assert_python_ok("-S", "-c", script)
7 changes: 7 additions & 0 deletions Lib/test/test_annotationlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@
)

from test import support
from test.support import import_helper
from test.test_inspect import inspect_stock_annotations
from test.test_inspect import inspect_stringized_annotations
from test.test_inspect import inspect_stringized_annotations_2
Expand Down Expand Up @@ -1367,3 +1368,9 @@ def test_multiple_ways_to_create(self):
class TestAnnotationLib(unittest.TestCase):
def test__all__(self):
support.check__all__(self, annotationlib)

def test_lazy_imports(self):
import_helper.ensure_lazy_imports("annotationlib", {
"typing",
"warnings",
})
9 changes: 9 additions & 0 deletions Lib/test/test_typing.py
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Expand Up @@ -6317,6 +6317,15 @@ def test_collect_parameters(self):
typing._collect_parameters
self.assertEqual(cm.filename, __file__)

def test_lazy_import(self):
import_helper.ensure_lazy_imports("typing", {
"warnings",
"inspect",
"re",
"contextlib",
# "annotationlib", # TODO

JelleZijlstra Apr 16, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

#132596 will fix this
})


@lru_cache()
def cached_func(x, y):
Expand Down
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