Python: how to access an attribute from a getattribute method

Question

I have the following class:

class StrLogger(str):
    def __init__(self, *args):
        self._log_ = []
        str.__init__(self, *args)
    def __getattribute__(self, attr):
        self._log_.append((self.__name__, attr))
        return str.__getattribute__(self, attr)

I can initialize a StrLogger with slog = StrLogger('foo') and I can access all of its inherited methods from str and it runs with no problem. The problem is, when I try to retreive the log with either slog._log_ or slog.__dict__['_log_'], the __getattribute__ method gets stuck in an infinite recursion. I understand why this is happening but my question is, how can I access the log?

Dietrich Epp · Accepted Answer · 2012-06-21 21:57:58Z

3

I can think of one way. Use object.__getattribute__ (or whatever your superclass is) whenever you need to bypass your customized attribute access.

class C(object):
    def __init__(self):
        self._log = []
    def __getattribute__(self, attr):
        _log = object.__getattribute__(self, '_log')
        _log.append(attr)
        return object.__getattribute__(self, attr)

>>> a = C()
>>> a.x = 1
>>> a.x
1
>>> a._log
['x', '_log']

answered Jun 21, 2012 at 21:57

Dietrich Epp

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Comments

Vinay Sajip · Accepted Answer · 2012-06-21 22:05:58Z

2

The following slightly modified class works:

class StrLogger(str):
    def __init__(self, *args):
        self._log_ = []
        str.__init__(self, *args)

    def __getattribute__(self, attr):
        log = str.__getattribute__(self, '_log_')
        cls = str.__getattribute__(self, '__class__')
        name = cls.__name__
        log.append((name, attr))
        return str.__getattribute__(self, attr)

s = StrLogger('abc')
print(s.title())
print(s.lower())
print(s.upper())
print(s.__dict__)

Running it results in

Abc
abc
ABC
{'_log_': [('StrLogger', 'title'), ('StrLogger', 'lower'), ('StrLogger', 'upper'), ('StrLogger', '__dict__')]}

answered Jun 21, 2012 at 22:05

Vinay Sajip

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Comments

glglgl · Accepted Answer · 2012-06-21 21:57:30Z

1

Your __getattribute__ should exclude __dict__ and maybe as well _log_ from logging. Alternatively, you could do something like

slog = StrLogger('foo')
thelog = slog._log_
do_stuff_with(slog)
print thelog

(untested!)

answered Jun 21, 2012 at 21:57

glglgl

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1 Comment

Matt Over a year ago

Thank you! I see now the recursion was caused by accessing _log_ during the logging. It still puzzles me that the logging itself worked when other attributes were accessed.

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