Python: Class as var dump error

Question

I'm trying to make a VarDump class, where I can do:

vd.attribute = value

and

print vd.attribute

So, this is the code:

class VarDump:

    def __init__(self):
        self.dump={}

    def __setattr__(self,item,var):
        self.dump[item]=var

    def __getattr__(self,item):
        if not item in self.dump: return ""
        return self.dump[item]

vd = VarDump()
vd.foo="bar"
print vd.foo

But I'm getting this error:

File "classAsVarDump.py", line 9, in __getattr__
    if not item in self.dump: return ""
RuntimeError: maximum recursion depth exceeded

Actually, if that's all you need, `class VarDump(object): pass` is sufficient. — Kimvais, Jul 30 '13 at 20:00

score 2 · Accepted Answer · answered Jul 30 '13 at 20:01

self.dump={} calls __setattr__ to set dump, which calls __getattr__ to get the dump to put dump into, which calls __getattr__ to get the dump, etc. You could resolve this with object.__setattr__, but the easier way is to just do this:

class Namespace(object):
    def __getattr__(self, attr):
        return ''

__getattr__ is only called when the attribute isn't found by normal means, so this doesn't need to handle looking up attributes that have actually been set.

score 2 · Answer 2 · answered Jul 30 '13 at 20:06

In Python 3.3, use the new types.SimpleNamespace() type instead:

>>> from types import SimpleNamespace
>>> vd = SimpleNamespace()
>>> vd.foo = 'bar'
>>> print(vd.foo)
bar

The documentation gives you a backwards-compatible version on a platter:

class SimpleNamespace:
    def __init__(self, **kwargs):
        self.__dict__.update(kwargs)
    def __repr__(self):
        keys = sorted(self.__dict__)
        items = ("{}={!r}".format(k, self.__dict__[k]) for k in keys)
        return "{}({})".format(type(self).__name__, ", ".join(items))

The only difference between your version and this one is that this one doesn't use __setattr__ and __getattr__ (not needed at all), this version takes initial values in the initializer, and it includes a nice representation:

>>> vd
namespace(foo='bar')

@NacibNeme: That's why I included the backwards-compatible Python version right here in the answer. It works directly on Python 2.7. — Martijn Pieters, Jul 30 '13 at 20:11

score 0 · Answer 3 · answered Jul 30 '13 at 20:01

0

No need to override __setattr__ or __getattr__

>>> class VarDump(object):
...     pass
... 
>>> c = VarDump()
>>> c.bar = 2
>>> print c.bar
2

answered Jul 30 '13 at 20:01

Kimvais

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The problem is that I don't want they to be written to self.__dict__ – Nacib Neme Jul 30 '13 at 20:12

Python: Class as var dump error

3 Answers3