8000 Close #13266: Add inspect.unwrap · python/cpython@e8c45d6 · GitHub
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Close #13266: Add inspect.unwrap
Initial patch by Daniel Urban and Aaron Iles
1 parent 7757820 commit e8c45d6

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‎Doc/library/inspect.rst

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@@ -797,6 +797,23 @@ Classes and functions
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.. versionadded:: 3.3
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.. function:: unwrap(func, *, stop=None)
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Get the object wrapped by *func*. It follows the chain of :attr:`__wrapped__`
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attributes returning the last object in the chain.
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*stop* is an optional callback accepting an object in the wrapper chain
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as its sole argument that allows the unwrapping to be terminated early if
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the callback returns a true value. If the callback never returns a true
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value, the last object in the chain is returned as usual. For example,
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:func:`signature` uses this to stop unwrapping if any object in the
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chain has a ``__signature__`` attribute defined.
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:exc:`ValueError` is raised if a cycle is encountered.
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.. versionadded:: 3.4
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.. _inspect-stack:
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The interpreter stack

‎Doc/whatsnew/3.4.rst

Lines changed: 11 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -185,6 +185,15 @@ functools
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New :func:`functools.single 8000 dispatch` decorator: see the :pep:`443`.
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inspect
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-------
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:func:`~inspect.unwrap` makes it easy to unravel wrapper function chains
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created by :func:`functools.wraps` (and any other API that sets the
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``__wrapped__`` attribute on a wrapper function).
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smtplib
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-------
190199

@@ -327,6 +336,5 @@ that may require changes to your code.
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wrapped attribute set. This means ``__wrapped__`` attributes now correctly
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link a stack of decorated functions rather than every ``__wrapped__``
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attribute in the chain referring to the innermost function. Introspection
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libraries that assumed the previous behaviour was intentional will need to
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be updated to walk the chain of ``__wrapped__`` attributes to find the
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innermost function.
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libraries that assumed the previous behaviour was intentional can use
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:func:`inspect.unwrap` to gain equivalent behaviour.

‎Lib/inspect.py

Lines changed: 37 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -360,6 +360,40 @@ def getmro(cls):
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"Return tuple of base classes (including cls) in method resolution order."
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return cls.__mro__
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# -------------------------------------------------------- function helpers
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def unwrap(func, *, stop=None):
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"""Get the object wrapped by *func*.
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Follows the chain of :attr:`__wrapped__` attributes returning the last
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object in the chain.
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*stop* is an optional callback accepting an object in the wrapper chain
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as its sole argument that allows the unwrapping to be terminated early if
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the callback returns a true value. If the callback never returns a true
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value, the last object in the chain is returned as usual. For example,
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:func:`signature` uses this to stop unwrapping if any object in the
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chain has a ``__signature__`` attribute defined.
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:exc:`ValueError` is raised if a cycle is encountered.
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"""
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if stop is None:
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def _is_wrapper(f):
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return hasattr(f, '__wrapped__')
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else:
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def _is_wrapper(f):
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return hasattr(f, '__wrapped__') and not stop(f)
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f = func # remember the original func for error reporting
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memo = {id(f)} # Memoise by id to tolerate non-hashable objects
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while _is_wrapper(func):
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func = func.__wrapped__
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id_func = id(func)
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if id_func in memo:
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raise ValueError('wrapper loop when unwrapping {!r}'.format(f))
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memo.add(id_func)
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return func
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# -------------------------------------------------- source code extraction
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def indentsize(line):
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"""Return the indent size, in spaces, at the start of a line of text."""
@@ -1346,6 +1380,9 @@ def signature(obj):
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sig = signature(obj.__func__)
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return sig.replace(parameters=tuple(sig.parameters.values())[1:])
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# Was this function wrapped by a decorator?
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obj = unwrap(obj, stop=(lambda f: hasattr(f, "__signature__")))
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try:
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sig = obj.__signature__
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except AttributeError:
@@ -1354,13 +1391,6 @@ def signature(obj):
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if sig is not None:
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return sig
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1357-
try:
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# Was this function wrapped by a decorator?
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wrapped = obj.__wrapped__
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except AttributeError:
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pass
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else:
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return signature(wrapped)
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13651395
if isinstance(obj, types.FunctionType):
13661396
return Signature.from_function(obj)

‎Lib/test/test_inspect.py

Lines changed: 73 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,6 +8,7 @@
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import collections
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import os
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import shutil
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import functools
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from os.path import normcase
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from test.support import run_unittest, TESTFN, DirsOnSysPath
@@ -1719,6 +1720,17 @@ def __call__(self, a, b):
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((('b', ..., ..., "positional_or_keyword"),),
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...))
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# Test we handle __signature__ partway down the wrapper stack
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def wrapped_foo_call():
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pass
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wrapped_foo_call.__wrapped__ = Foo.__call__
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self.assertEqual(self.signature(wrapped_foo_call),
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((('a', ..., ..., "positional_or_keyword"),
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('b', ..., ..., "positional_or_keyword")),
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...))
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17221734
def test_signature_on_class(self):
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class C:
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def __init__(self, a):
@@ -1833,6 +1845,10 @@ class Wrapped:
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self.assertEqual(self.signature(Wrapped),
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((('a', ..., ..., "positional_or_keyword"),),
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...))
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# wrapper loop:
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Wrapped.__wrapped__ = Wrapped
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with self.assertRaisesRegex(ValueError, 'wrapper loop'):
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self.signature(Wrapped)
18361852

18371853
def test_signature_on_lambdas(self):
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self.assertEqual(self.signature((lambda a=10: a)),
@@ -2284,14 +2300,70 @@ def bar(b): pass
22842300
self.assertNotEqual(ba, ba4)
22852301

22862302

2303+
class TestUnwrap(unittest.TestCase):
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def test_unwrap_one(self):
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def func(a, b):
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return a + b
2308+
wrapper = functools.lru_cache(maxsize=20)(func)
2309+
self.assertIs(inspect.unwrap(wrapper), func)
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2311+
def test_unwrap_several(self):
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def func(a, b):
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return a + b
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wrapper = func
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for __ in range(10):
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@functools.wraps(wrapper)
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def wrapper():
2318+
pass
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self.assertIsNot(wrapper.__wrapped__, func)
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self.assertIs(inspect.unwrap(wrapper), func)
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2322+
def test_stop(self):
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def func1(a, b):
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return a + b
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@functools.wraps(func1)
2326+
def func2():
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pass
2328+
@functools.wraps(func2)
2329+
def wrapper():
2330+
pass
2331+
func2.stop_here = 1
2332+
unwrapped = inspect.unwrap(wrapper,
2333+
stop=(lambda f: hasattr(f, "stop_here")))
2334+
self.assertIs(unwrapped, func2)
2335+
2336+
def test_cycle(self):
2337+
def func1(): pass
2338+
func1.__wrapped__ = func1
2339+
with self.assertRaisesRegex(ValueError, 'wrapper loop'):
2340+
inspect.unwrap(func1)
2341+
2342+
def func2(): pass
2343+
func2.__wrapped__ = func1
2344+
func1.__wrapped__ = func2
2345+
with self.assertRaisesRegex(ValueError, 'wrapper loop'):
2346+
inspect.unwrap(func1)
2347+
with self.assertRaisesRegex(ValueError, 'wrapper loop'):
2348+
inspect.unwrap(func2)
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2350+
def test_unhashable(self):
2351+
def func(): pass
2352+
func.__wrapped__ = None
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class C:
2354+
__hash__ = None
2355+
__wrapped__ = func
2356+
self.assertIsNone(inspect.unwrap(C()))
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22872359
def test_main():
22882360
run_unittest(
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TestDecorators, TestRetrievingSourceCode, TestOneliners, TestBuggyCases,
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TestInterpreterStack, TestClassesAndFunctions, TestPredicates,
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TestGetcallargsFunctions, TestGetcallargsMethods,
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TestGetcallargsUnboundMethods, TestGetattrStatic, TestGetGeneratorState,
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TestNoEOL, TestSignatureObject, TestSignatureBind, TestParameterObject,
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TestBoundArguments, TestGetClosureVars
2366+
TestBoundArguments, TestGetClosureVars, TestUnwrap
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)
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22972369
if __name__ == "__main__":

‎Misc/NEWS

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@@ -171,6 +171,9 @@ Core and Builtins
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Library
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-------
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- Issue #13266: Added inspect.unwrap to easily unravel __wrapped__ chains
175+
(initial patch by Daniel Urban and Aaron Iles)
176+
174177
- Issue #18561: Skip name in ctypes' _build_callargs() if name is NULL.
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176179
- Issue #18559: Fix NULL pointer dereference error in _pickle module

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