Python: Class as var dump error [duplicate]

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
– Kimvais, Commented Jul 30, 2013 at 20:00

user2357112 · Accepted Answer · 2013-07-30 20:01:24Z

2

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.

answered Jul 30, 2013 at 20:01

user2357112

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Comments

Martijn Pieters · Accepted Answer · 2013-07-30 20:06:40Z

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.

Kimvais · Accepted Answer · 2013-07-30 20:01:35Z

0

No need to override __setattr__ or __getattr__

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

answered Jul 30, 2013 at 20:01

Kimvais

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1 Comment

Nacib Neme Over a year ago

The problem is that I don't want they to be written to self.__dict__

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