Lib/unittest/__init__.py

cpython 3.14 @ ab2d84fe1023/Lib/unittest/__init__.py ↗

The unittest package exposes its full public API through this single init module. It re-exports every name from its sub-modules so that callers only need import unittest rather than importing individual submodules directly. The file is intentionally thin: its job is assembly, not logic.

Map

Lines	Symbol	Role
47-52	__all__	Canonical list of exported public names
54	__unittest	Sentinel that suppresses this file from test tracebacks
56-69	import block	Pulls symbols from result, case, suite, loader, main, runner, signals
72-73	__dir__	Adds IsolatedAsyncioTestCase to dir(unittest) without importing it
75-80	__getattr__	Lazy-loads IsolatedAsyncioTestCase from .async_case on first access

Reading

The __all__ list and re-exports

__all__ declares the authoritative contract for from unittest import *. Every name listed there has a corresponding binding in the import block below it.

# CPython: Lib/unittest/__init__.py:47 __all__
__all__ = ['TestResult', 'TestCase', 'IsolatedAsyncioTestCase', 'TestSuite',
           'TextTestRunner', 'TestLoader', 'FunctionTestCase', 'main',
           'defaultTestLoader', 'SkipTest', 'skip', 'skipIf', 'skipUnless',
           'expectedFailure', 'TextTestResult', 'installHandler',
           'registerResult', 'removeResult', 'removeHandler',
           'addModuleCleanup', 'doModuleCleanups', 'enterModuleContext']

The four foundational classes (TestCase, TestSuite, TestLoader, TestResult) come from separate sub-modules but are surfaced here so user code never has to reach into unittest.case or unittest.loader directly. defaultTestLoader is the singleton instance of TestLoader that unittest.main() uses when no explicit loader is passed.

# CPython: Lib/unittest/__init__.py:56 import block
from .result import TestResult
from .case import (addModuleCleanup, TestCase, FunctionTestCase, SkipTest, skip,
                   skipIf, skipUnless, expectedFailure, doModuleCleanups,
                   enterModuleContext)
from .suite import BaseTestSuite, TestSuite
from .loader import TestLoader, defaultTestLoader
from .main import TestProgram, main
from .runner import TextTestRunner, TextTestResult
from .signals import installHandler, registerResult, removeResult, removeHandler

The __unittest traceback sentinel

# CPython: Lib/unittest/__init__.py:54 __unittest
__unittest = True

Every unittest sub-module sets this module-level variable. The traceback formatter in result.py checks for it and hides frames from these files when printing test failures, so users see their own code rather than framework internals.

Lazy async import via __getattr__

IsolatedAsyncioTestCase pulls in asyncio at import time, so loading it eagerly would slow down every program that imports unittest. PEP 562 module __getattr__ defers that cost until the name is first accessed.

# CPython: Lib/unittest/__init__.py:75 __getattr__
def __getattr__(name):
    if name == 'IsolatedAsyncioTestCase':
        global IsolatedAsyncioTestCase
        from .async_case import IsolatedAsyncioTestCase
        return IsolatedAsyncioTestCase
    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

The global statement caches the result so the import fires only once. __dir__ at line 72 ensures IsolatedAsyncioTestCase appears in dir(unittest) even before __getattr__ has run.

gopy notes

Status: not yet ported.

Planned package path: module/unittest/.

The init module itself requires no Go logic. It will be shipped as a pure-Python file loaded from the stdlib bundle, once the sub-modules (case, suite, loader, result, runner) are ported. The __unittest traceback-filter sentinel must be respected by the gopy traceback formatter when printing test failure output. The IsolatedAsyncioTestCase lazy-load can be deferred indefinitely since gopy does not yet support asyncio.