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bpo-40897:Give priority to using the current class constructor in inspect.signature #23336

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bpo-40897:Give priority to using the current class constructor in inspect.signature #23336

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37 changes: 17 additions & 20 deletions Lib/inspect.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2351,34 +2351,31 @@ def _signature_from_callable(obj, *,
sig = None
if isinstance(obj, type):
# obj is a class or a metaclass

create_method = None
# First, let's see if it has an overloaded __call__ defined
# in its metaclass
call = _signature_get_user_defined_method(type(obj), '__call__')
if call is not None:
create_method = call
else:
new = _signature_get_user_defined_method(obj, '__new__')
init = _signature_get_user_defined_method(obj, '__init__')
# Give priority to using the current class constructor
if '__new__' in obj.__dict__:
create_method = new
elif '__init__' in obj.__dict__:
create_method = init
elif new is not None:
create_method = new
elif init is not None:
create_method = init

if create_method is not None:
sig = _signature_from_callable(
call,
create_method,
follow_wrapper_chains=follow_wrapper_chains,
skip_bound_arg=skip_bound_arg,
sigcls=sigcls)
else:
# Now we check if the 'obj' class has a '__new__' method
new = _signature_get_user_defined_method(obj, '__new__')
if new is not None:
sig = _signature_from_callable(
new,
follow_wrapper_chains=follow_wrapper_chains,
skip_bound_arg=skip_bound_arg,
sigcls=sigcls)
else:
# Finally, we should have at least __init__ implemented
init = _signature_get_user_defined_method(obj, '__init__')
if init is not None:
sig = _signature_from_callable(
init,
follow_wrapper_chains=follow_wrapper_chains,
skip_bound_arg=skip_bound_arg,
sigcls=sigcls)

if sig is None:
# At this point we know, that `obj` is a class, with no user-
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19 changes: 19 additions & 0 deletions Lib/test/test_inspect.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2934,6 +2934,25 @@ def __init__(self, b):
('bar', 2, ..., "keyword_only")),
...))

def test_signature_on_subclass(self):
class A:
def __new__(cls, a=1, *args, **kwargs):
return object.__new__(cls)
class B(A):
def __init__(self, b):
pass
class C(A):
pass

self.assertEqual(self.signature(B),
((('b', ..., ..., "positional_or_keyword"),),
...))
self.assertEqual(self.signature(C),
((('a', 1, ..., 'positional_or_keyword'),
('args', ..., ..., 'var_positional'),
('kwargs', ..., ..., 'var_keyword')),
...))

@unittest.skipIf(MISSING_C_DOCSTRINGS,
"Signature information for builtins requires docstrings")
def test_signature_on_class_without_init(self):
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2020-11-17-16-40-31.bpo-40897.aveAre.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Give priority to using the current class constructor in
:func:`inspect.signature`. Patch by Weipeng Hong.