New submission from Komiya Takeshi <i.tkom...@gmail.com>:
inspect.signature() raises RuntimeError on failed to resolve the default
argument value. For example, it fails to inspect a subclass of
io.BufferedReader:
Example:
```
import inspect
import io
class MyBufferedReader(io.BufferedReader):
"""buffer reader class."""
inspect.signature(MyBufferedReader)
```
Result:
```
Traceback (most recent call last):
File "/Users/tkomiya/.pyenv/versions/3.9.1/lib/python3.9/inspect.py", line
2042, in wrap_value
value = eval(s, module_dict)
File "<string>", line 1, in <module>
NameError: name 'DEFAULT_BUFFER_SIZE' is not defined
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/Users/tkomiya/.pyenv/versions/3.9.1/lib/python3.9/inspect.py", line
2045, in wrap_value
value = eval(s, sys_module_dict)
File "<string>", line 1, in <module>
NameError: name 'DEFAULT_BUFFER_SIZE' is not defined
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/Users/tkomiya/work/tmp/doc/example.py", line 9, in <module>
inspect.signature(MyBufferedReader)
File "/Users/tkomiya/.pyenv/versions/3.9.1/lib/python3.9/inspect.py", line
3130, in signature
return Signature.from_callable(obj, follow_wrapped=follow_wrapped)
File "/Users/tkomiya/.pyenv/versions/3.9.1/lib/python3.9/inspect.py", line
2879, in from_callable
return _signature_from_callable(obj, sigcls=cls,
File "/Users/tkomiya/.pyenv/versions/3.9.1/lib/python3.9/inspect.py", line
2397, in _signature_from_callable
return _signature_fromstr(sigcls, obj, text_sig)
File "/Users/tkomiya/.pyenv/versions/3.9.1/lib/python3.9/inspect.py", line
2095, in _signature_fromstr
p(name, default)
File "/Users/tkomiya/.pyenv/versions/3.9.1/lib/python3.9/inspect.py", line
2077, in p
default_node = RewriteSymbolics().visit(default_node)
File "/Users/tkomiya/.pyenv/versions/3.9.1/lib/python3.9/ast.py", line 407,
in visit
return visitor(node)
File "/Users/tkomiya/.pyenv/versions/3.9.1/lib/python3.9/inspect.py", line
2069, in visit_Name
return wrap_value(node.id)
File "/Users/tkomiya/.pyenv/versions/3.9.1/lib/python3.9/inspect.py", line
2047, in wrap_value
raise RuntimeError()
RuntimeError
```
In my investigation, inspect.signature() tries to evaluate the default argument
value of the class constructor. But it fails to evaluate because of the 2nd
argument of the constructor takes a constant; `DEFAULT_BUFFER_SIZE`, but it is
not found on the current context.
I think it would be better to search the constants for the modules of the base
classes. I just made a simple patch to resolve this bug.
----------
components: Library (Lib)
files: inspect.patch
keywords: patch
messages: 386212
nosy: i.tkomiya
priority: normal
severity: normal
status: open
title: inspect.signature() raises RuntimeError on failed to resolve the default
argument value
versions: Python 3.10, Python 3.6, Python 3.7, Python 3.8, Python 3.9
Added file: https://bugs.python.org/file49788/inspect.patch
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue43118>
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