logilab-astng #19641 "maximum recursion depth exceeded" messages w/ python 2.6 [validation pending]

Daniel Harding reported on python-projects.

This past June problems were reported with seeing messages like the following on stderr when running pylint:

Exception RuntimeError: 'maximum recursion depth exceeded while
calling a Python object' in <type 'exceptions.AttributeError'>
ignored

At the time it was attributed to a bug in Python 2.6.2. However, after upgrading to Python 2.6.4 I still saw the problem, so decided to investigate further, and eventually tracked it down to an infinite recursion in logilab-astng

I have attached a Python file which triggers the problem. The call stack which produces the message is as follows:

0  File "C:\Python26\Scripts\pylint.bat", line 12, in <module>
     lint.Run(sys.argv[1:])
1  File "C:\Python26\lib\site-packages\pylint-0.18.1-py2.6.egg\pylint\lint.py", line 884, in __init__
     linter.check(args)
2  File "C:\Python26\lib\site-packages\pylint-0.18.1-py2.6.egg\pylint\lint.py", line 501, in check
    self.check_astng_module(astng, checkers)
3  File "C:\Python26\lib\site-packages\pylint-0.18.1-py2.6.egg\pylint\lint.py", line 578, in check_astng_module
     if implements(checker, IASTNGChecker)])
4  File "C:\Python26\lib\site-packages\pylint-0.18.1-py2.6.egg\pylint\lint.py", line 595, in astng_events
     self.astng_events(child, checkers, _reversed_checkers)
5  File "C:\Python26\lib\site-packages\pylint-0.18.1-py2.6.egg\pylint\lint.py", line 595, in astng_events
     self.astng_events(child, checkers, _reversed_checkers)
6  File "C:\Python26\lib\site-packages\pylint-0.18.1-py2.6.egg\pylint\lint.py", line 592, in astng_events
     checker.visit(astng)
7  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\utils.py", line 320, in visit
     method(node)
8  File "C:\Python26\lib\site-packages\pylint-0.18.1-py2.6.egg\pylint\checkers\typecheck.py", line 207, in visit_callfunc
     called = safe_infer(node.func)
9  File "C:\Python26\lib\site-packages\pylint-0.18.1-py2.6.egg\pylint\checkers\utils.py", line 38, in safe_infer
     value = inferit.next()
10  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\infutils.py", line 203, in wrapped
     for res in _func(node, context, **kwargs):
11  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\infutils.py", line 231, in wrapper
     for node in func(*args, **kwargs):
12  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\inference.py", line 281, in infer_getattr
     for obj in owner.igetattr(self.attrname, context):
13  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\infutils.py", line 265, in igetattr
     self._wrap_attr(self.getattr(name, context, lookupclass=False), context),
14  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\infutils.py", line 248, in getattr
     return self._proxied.instance_attr(name, context)
15  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\inference.py", line 53, in _set_proxied
     if not hasattr(const, '__proxied'):
16  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\infutils.py", line 44, in __getattr__
     return getattr(self._proxied, name)
17  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\inference.py", line 53, in _set_proxied
     if not hasattr(const, '__proxied'):
18  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\infutils.py", line 44, in __getattr__
     return getattr(self._proxied, name)
19  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\inference.py", line 53, in _set_proxied
     if not hasattr(const, '__proxied'):
20  File "C:\Python26\lib\site-packages\logilab_astng-0.19.1-py2.6.egg\logilab\astng\infutils.py", line 44, in __getattr__
     return getattr(self._proxied, name)

and so on...

What is happening is that Instance.getattr (entry 14 in the call stack) is accessing the _proxied attribute of the node. This attribute is actually a property whose getter is the _set_proxied function (entry 15 in the call stack). The first thing this function does is call hasattr on the node to see if it has a __proxied attribute. Because this attribute does not yet exist on the node, the node's __getattr__ method is invoked (entry 16 in the call stack). It in turn attempts to call getattr on its _proxied attribute. This in turn invokes the _proxied property's _set_proxied function (entry 17 in the call stack), resulting in infinite recursion.

To reproduce, run

pylint -r n -f parseable bug.py

on the attached bug.py. I've also attached my .pylintrc.

Here's the output from running pylint --version on my system:

pylint.bat 0.18.1,
astng 0.19.1, common 0.45.2
Python 2.6.4 (r264:75708, Oct 26 2009, 08:23:19) [MSC v.1500 32 bit (Intel)]

I don't understand what the inference system is doing well enough to know how to fix the problem, but hopefully this will give someone enough information to work on it.