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[3.10] gh-85267: Improvements to inspect.signature __text_signature__…
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… handling (GH-98796) (#100393)

This makes a couple related changes to inspect.signature's behaviour
when parsing a signature from `__text_signature__`.

First, `inspect.signature` is documented as only raising ValueError or
TypeError. However, in some cases, we could raise RuntimeError.  This PR
changes that, thereby fixing GH-83685.

(Note that the new ValueErrors in RewriteSymbolics are caught and then
reraised with a message)

Second, `inspect.signature` could randomly drop parameters that it
didn't understand (corresponding to `return None` in the `p` function).
This is the core issue in GH-85267. I think this is very surprising
behaviour and it seems better to fail outright.

Third, adding this new failure broke a couple tests. To fix them (and to
e.g. allow `inspect.signature(select.epoll.register)` as in GH-85267), I
add constant folding of a couple binary operations to RewriteSymbolics.

(There's some discussion of making signature expression evaluation
arbitrary powerful in GH-68155. I think that's out of scope. The
additional constant folding here is pretty straightforward, useful, and
not much of a slippery slope)

Fourth, while GH-85267 is incorrect about the cause of the issue, it turns
out if you had consecutive newlines in __text_signature__, you'd get
`tokenize.TokenError`.

Finally, the `if name is invalid:` code path was dead, since
`parse_name` never returned `invalid`..
(cherry picked from commit 79311cb)

Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
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hauntsaninja authored Dec 21, 2022
1 parent 561e15b commit 919045c
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Showing 3 changed files with 47 additions and 13 deletions.
33 changes: 21 additions & 12 deletions Lib/inspect.py
Original file line number Diff line number Diff line change
Expand Up @@ -2061,7 +2061,7 @@ def _signature_strip_non_python_syntax(signature):
self_parameter = None
last_positional_only = None

lines = [l.encode('ascii') for l in signature.split('\n')]
lines = [l.encode('ascii') for l in signature.split('\n') if l]
generator = iter(lines).__next__
token_stream = tokenize.tokenize(generator)

Expand Down Expand Up @@ -2141,7 +2141,6 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):

parameters = []
empty = Parameter.empty
invalid = object()

module = None
module_dict = {}
Expand All @@ -2165,11 +2164,11 @@ def wrap_value(s):
try:
value = eval(s, sys_module_dict)
except NameError:
raise RuntimeError()
raise ValueError

if isinstance(value, (str, int, float, bytes, bool, type(None))):
return ast.Constant(value)
raise RuntimeError()
raise ValueError

class RewriteSymbolics(ast.NodeTransformer):
def visit_Attribute(self, node):
Expand All @@ -2179,7 +2178,7 @@ def visit_Attribute(self, node):
a.append(n.attr)
n = n.value
if not isinstance(n, ast.Name):
raise RuntimeError()
raise ValueError
a.append(n.id)
value = ".".join(reversed(a))
return wrap_value(value)
Expand All @@ -2189,19 +2188,29 @@ def visit_Name(self, node):
raise ValueError()
return wrap_value(node.id)

def visit_BinOp(self, node):
# Support constant folding of a couple simple binary operations
# commonly used to define default values in text signatures
left = self.visit(node.left)
right = self.visit(node.right)
if not isinstance(left, ast.Constant) or not isinstance(right, ast.Constant):
raise ValueError
if isinstance(node.op, ast.Add):
return ast.Constant(left.value + right.value)
elif isinstance(node.op, ast.Sub):
return ast.Constant(left.value - right.value)
elif isinstance(node.op, ast.BitOr):
return ast.Constant(left.value | right.value)
raise ValueError

def p(name_node, default_node, default=empty):
name = parse_name(name_node)
if name is invalid:
return None
if default_node and default_node is not _empty:
try:
default_node = RewriteSymbolics().visit(default_node)
o = ast.literal_eval(default_node)
default = ast.literal_eval(default_node)
except ValueError:
o = invalid
if o is invalid:
return None
default = o if o is not invalid else default
raise ValueError("{!r} builtin has invalid signature".format(obj)) from None
parameters.append(Parameter(name, kind, default=default, annotation=empty))

# non-keyword-only parameters
Expand Down
21 changes: 20 additions & 1 deletion Lib/test/test_inspect.py
Original file line number Diff line number Diff line change
Expand Up @@ -2477,7 +2477,7 @@ def p(name): return signature.parameters[name].default
self.assertEqual(p('f'), False)
self.assertEqual(p('local'), 3)
self.assertEqual(p('sys'), sys.maxsize)
self.assertNotIn('exp', signature.parameters)
self.assertEqual(p('exp'), sys.maxsize - 1)

test_callable(object)

Expand Down Expand Up @@ -4246,10 +4246,29 @@ def func(*args, **kwargs):
sig = inspect.signature(func)
self.assertIsNotNone(sig)
self.assertEqual(str(sig), '(self, /, a, b=1, *args, c, d=2, **kwargs)')

func.__text_signature__ = '($self, a, b=1, /, *args, c, d=2, **kwargs)'
sig = inspect.signature(func)
self.assertEqual(str(sig), '(self, a, b=1, /, *args, c, d=2, **kwargs)')

func.__text_signature__ = '(self, a=1+2, b=4-3, c=1 | 3 | 16)'
sig = inspect.signature(func)
self.assertEqual(str(sig), '(self, a=3, b=1, c=19)')

func.__text_signature__ = '(self, a=1,\nb=2,\n\n\n c=3)'
sig = inspect.signature(func)
self.assertEqual(str(sig), '(self, a=1, b=2, c=3)')

func.__text_signature__ = '(self, x=does_not_exist)'
with self.assertRaises(ValueError):
inspect.signature(func)
func.__text_signature__ = '(self, x=sys, y=inspect)'
with self.assertRaises(ValueError):
inspect.signature(func)
func.__text_signature__ = '(self, 123)'
with self.assertRaises(ValueError):
inspect.signature(func)

def test_base_class_have_text_signature(self):
# see issue 43118
from test.ann_module7 import BufferedReader
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
Several improvements to :func:`inspect.signature`'s handling of ``__text_signature``.
- Fixes a case where :func:`inspect.signature` dropped parameters
- Fixes a case where :func:`inspect.signature` raised :exc:`tokenize.TokenError`
- Allows :func:`inspect.signature` to understand defaults involving binary operations of constants
- :func:`inspect.signature` is documented as only raising :exc:`TypeError` or :exc:`ValueError`, but sometimes raised :exc:`RuntimeError`. These cases now raise :exc:`ValueError`
- Removed a dead code path

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