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Add _check_SETATTR_TARGET_value and tests for it
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‎lazyimports/__init__.py‎

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@@ -40,9 +40,13 @@
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is_lazy,
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force_load,
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lazy,
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_check_SETATTR_TARGET_value
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)
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_check_SETATTR_TARGET_value()
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del _check_SETATTR_TARGET_value
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# License MIT <aiwonderland> in <2026>
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__version__ = "0.1.5"
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# License MIT <aiwonderland> in <2026>

‎lazyimports/core.py‎

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@@ -77,6 +77,81 @@
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API surface small. Change at your own risk and reset it before any
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code that expects the default behaviour runs."""
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# The set of legal values for ``SETATTR_TARGET``. Exposed as a
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# module-level constant so users can introspect the contract without
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# having to call the validator first. Treated as a tuple (immutable)
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# so accidental mutation cannot widen the accepted set.
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_VALID_SETATTR_TARGETS = ("module", "proxy")
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# License MIT <aiwonderland> in <2026>
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def _check_SETATTR_TARGET_value(value=None):
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"""Validate that ``value`` (or the current ``SETATTR_TARGET``)
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is one of the accepted modes for ``LazyModule.__setattr__``.
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This helper is the single source of truth for what counts as a
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legal ``SETATTR_TARGET`` value. It is invoked in two places:
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1. At import time, via the explicit ``_SETATTR_TARGET_VALIDATED``
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flag below, so a corrupted or mutated global is caught as
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early as possible.
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2. By :func:`set_SETATTR_TARGET`, the supported runtime entry
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point for changing the mode.
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Parameters
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----------
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value : str or None, optional
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The value to validate. If ``None`` (the default), the
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module-level ``SETATTR_TARGET`` constant itself is checked.
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Returns
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-------
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str
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The validated value, always one of ``"module"`` or
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``"proxy"``. Returning the value (instead of just raising on
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failure) lets callers use this function as a normaliser.
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Raises
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------
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TypeError
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If ``value`` is provided and is not a ``str``. The mode
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names are string literals; any other type is unambiguously
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a programming error.
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ValueError
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If ``value`` is a string but not in
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``_VALID_SETATTR_TARGETS``. The message lists every
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accepted value and echoes back what was received, which is
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enough information to fix the mistake without consulting
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the source.
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"""
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if value is None:
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value = SETATTR_TARGET
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if not isinstance(value, str):
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# Type errors are reported separately from value errors so
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# callers (and ``set_SETATTR_TARGET``) can decide which
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# exception to surface to the end user.
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raise TypeError(
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"SETATTR_TARGET must be a str, got {!r} of type {}".format(
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value, type(value).__name__,
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)
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)
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if value not in _VALID_SETATTR_TARGETS:
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accepted = ", ".join(
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"{!r}".format(v) for v in _VALID_SETATTR_TARGETS
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)
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raise ValueError(
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"SETATTR_TARGET must be one of: {}; got {!r}".format(
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accepted, value,
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)
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)
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return value
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# Run the validator once at import time so a broken module-level
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# value fails fast (at ``import lazyimports``) instead of silently
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# later. The result is intentionally discarded; we only care about
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# the side effect of raising on invalid input.
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_SETATTR_TARGET_VALIDATED = _check_SETATTR_TARGET_value()
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del _SETATTR_TARGET_VALIDATED
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# GNUv3 License, add in <2018>, by <Evan Yang>
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class LazyModule(types.ModuleType):
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"""Proxy module that defers the real import until attribute access.

‎test_lazyimports.py‎

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@@ -27,6 +27,7 @@
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SUPPORT_LAZY_IMPORT,
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SETATTR_TARGET,
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LazyModule,
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_check_SETATTR_TARGET_value,
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force_load,
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is_lazy,
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lazy,
@@ -626,5 +627,151 @@ def test_configuration_via_core_round_trips(self):
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delattr(math, "SCRATCH2")
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# License MIT <aiwonderland> in <2026>
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class TestCheckSetattrTargetValue(unittest.TestCase):
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"""Tests for ``_check_SETATTR_TARGET_value``.
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The validator is the single source of truth for what counts as a
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legal ``SETATTR_TARGET`` value. It must:
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* return the validated value (acting as a normaliser);
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* accept both ``"module"`` and ``"proxy"``;
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* reject unknown strings with ``ValueError``;
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* reject non-string arguments with ``TypeError``;
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* treat ``value=None`` as a request to re-check the current
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module-level ``SETATTR_TARGET``.
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"""
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def setUp(self):
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# Save and restore the global so an exception-raising test
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# does not leave the package in a broken state for the
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# tests that follow.
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self._previous_mode = core.SETATTR_TARGET
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def tearDown(self):
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core.SETATTR_TARGET = self._previous_mode
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if core.SETATTR_TARGET not in ("module", "proxy"):
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core.SETATTR_TARGET = "module"
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# ------------------------------------------------------------------
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# Happy path
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# ------------------------------------------------------------------
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def test_default_module_value_passes(self):
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# The shipped default must validate without raising. We
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# call without an argument so the function checks the
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# current ``SETATTR_TARGET``.
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result = _check_SETATTR_TARGET_value()
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self.assertEqual(result, SETATTR_TARGET)
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self.assertEqual(result, "module")
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def test_explicit_module_string(self):
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result = _check_SETATTR_TARGET_value("module")
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self.assertEqual(result, "module")
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def test_explicit_proxy_string(self):
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result = _check_SETATTR_TARGET_value("proxy")
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self.assertEqual(result, "proxy")
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def test_none_argument_validates_current_value(self):
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# ``None`` is documented as ``"check the current value"``,
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# not as "missing argument". This is a behaviour the tests
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# lock down so a future refactor cannot quietly change it.
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core.SETATTR_TARGET = "proxy"
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result = _check_SETATTR_TARGET_value(None)
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self.assertEqual(result, "proxy")
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core.SETATTR_TARGET = "module"
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result = _check_SETATTR_TARGET_value(None)
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self.assertEqual(result, "module")
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def test_returns_valid_value_for_use_as_normaliser(self):
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# The return value must equal the input when it is valid,
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# which lets callers use the function as a one-stop
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# ``str -> Literal[...]`` converter.
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self.assertEqual(_check_SETATTR_TARGET_value("module"), "module")
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self.assertEqual(_check_SETATTR_TARGET_value("proxy"), "proxy")
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# ------------------------------------------------------------------
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# Value errors
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# ------------------------------------------------------------------
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def test_unknown_string_raises_value_error(self):
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for bad in ("MODULE", "Module", "Module ", "", "modules", "prxy"):
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with self.subTest(value=bad):
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with self.assertRaises(ValueError):
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_check_SETATTR_TARGET_value(bad)
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def test_value_error_message_lists_accepted_values(self):
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# The message is part of the API surface: callers (and
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# automated tooling) rely on it being informative without
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# having to consult the source.
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try:
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_check_SETATTR_TARGET_value("nope")
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except ValueError as exc:
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message = str(exc)
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else:
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self.fail("ValueError not raised")
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# Both accepted values must appear in the message.
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self.assertIn("'module'", message)
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self.assertIn("'proxy'", message)
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# And the offending value must be echoed back so the
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# user can see what they sent.
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self.assertIn("'nope'", message)
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def test_value_error_with_none_checks_current(self):
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# If the *current* ``SETATTR_TARGET`` has been corrupted
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# before the test runs, the validator must still catch it.
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core.SETATTR_TARGET = "garbage"
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with self.assertRaises(ValueError):
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_check_SETATTR_TARGET_value(None)
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# ------------------------------------------------------------------
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# Type errors
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# ------------------------------------------------------------------
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def test_non_string_raises_type_error(self):
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for bad in (0, 1, 1.5, True, None, [], {}, (), b"module", object()):
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with self.subTest(value=bad, type=type(bad).__name__):
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# ``None`` is special-cased (means "check current
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# value") and should NOT raise ``TypeError``. Skip
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# it explicitly here.
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if bad is None:
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continue
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with self.assertRaises(TypeError):
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_check_SETATTR_TARGET_value(bad)
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def test_type_error_message_mentions_str(self):
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try:
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_check_SETATTR_TARGET_value(42)
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except TypeError as exc:
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message = str(exc)
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else:
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self.fail("TypeError not raised")
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# The error must point at ``str`` as the expected type so
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# users immediately know what to pass instead.
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self.assertIn("str", message)
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def test_subclass_of_str_is_accepted(self):
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# ``str`` subclasses are valid: this is standard Python
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# duck-typing and avoids surprising users who build their
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# own string-like types.
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class MyStr(str):
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pass
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self.assertEqual(_check_SETATTR_TARGET_value(MyStr("module")), "module")
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self.assertEqual(_check_SETATTR_TARGET_value(MyStr("proxy")), "proxy")
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# ------------------------------------------------------------------
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# Integration with the package import-time check
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# ------------------------------------------------------------------
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def test_package_loaded_successfully(self):
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# ``__init__.py`` calls ``_check_SETATTR_TARGET_value()``
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# once at import time. The mere fact that we have reached
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# this test class proves the call succeeded; if the
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# default value were invalid the import would have raised
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# before any test could run.
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#
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# We additionally assert the global is still in a valid
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# state after all the previous tests have potentially
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# poked at it.
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_check_SETATTR_TARGET_value() # must not raise
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if __name__ == "__main__":
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unittest.main(verbosity=2)

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