A.T.Hofkamp a écrit :
> Hello all,
>
> This morning I tried to create my own read-only dictionary, and failed
> miserably.
> I don't understand why, can somebody enlighten me?
>
> Below is a brute-force experiment that cannot deal with "x in obj", plz read
> the explanation below the code:
> --------------------------------
> class myowndict(object):
> def __init__(self, mydict):
> self.mydict = mydict
Why don't you just subclass dict and override the needed method(s) ?
class ReadOnlyDict(dict):
@classmethod
def _raise(cls):
raise AttributeError("%s is read-only" % cls.__name__)
def __setitem__(self, name, val):
self._raise()
def setdefault(self, name, value=None):
self._raise()
# TODO : check if I missed some other setter ?
def test(d):
print d
try:
d['c'] = 3
except AttributeError, e:
print "__setitem__ ok, got : %s" % e
else:
assert('failed on __setitem__')
try:
d.setdefault('c', 3)
except AttributeError, e:
print "setdefault ok, got : %s" % e
else:
assert('failed on setdefault')
if __name__ == '__main__':
d1 = ReadOnlyDict(a=1, b=2)
test(d1)
d2 = ReadOnlyDict({'a':1, 'b':2})
test(d2)
d3 = ReadOnlyDict((c, i+1) for i, c in enumerate('ab'))
test(d3)
d4 = ReadOnlyDict(**d1)
test(d4)
NB : works fine so far, but choke on fromkeys, which obviously uses
__setitem__
> # Below is produced with
> # print '\n'.join([' self.%s = self.mydict.%s' % (v,v)
> # for v in dir(dict)])
> # commented-out functions done by hand
> #
> #self.__class__ = self.mydict.__class__
> self.__cmp__ = self.mydict.__cmp__
> self.__contains__ = self.mydict.__contains__
(snip lots of useless code)
May I suggest that you learn to use __getattr__ and __setattr__ ?-)
HTH
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