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Comments on A class to access dicts using attribute syntax
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A class to access dicts using attribute syntax
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I've written a class that allows to access dictionary entries of arbitrary dicts with appropriate string keys through attribute access syntax on an instance of the class.
My questions are:
-
Is this class a good idea to begin with?
-
Is there anything that should be done differently?
Here's the class:
class DictProxy:
"""
Allow to access a dictionary through attribute access syntax.
Obviously only dictionary entries whose keys are strings
conforming to identifier rules can be accessed this way; also,
identifiers starting with underscore are not delegated to the
dictionary (thus dictionary entries whose key starts with
underscore cannot be accessed this way).
"""
def __init__(self, dictionary):
"""
Initialize the DictProxy with a dictionary
"""
self._dictionary = dictionary
def __setattr__(self, name, value):
"""
Redirect non-underscore attribute assignments to dictionary updates
"""
if name[0] == "_":
super().__setattr__(name, value)
else:
self._dictionary[name] = value
def __getattr__(self, name):
"""
Redirect non-underscore attribute reads to dictionary reads
"""
if name[0] == "_":
return super().__getattr__(name)
else:
try:
return self._dictionary[name]
except KeyError as error:
# hasattr fails if the exception isn't an AttributeError
raise AttributeError(error)
def __delattr__(self, name):
"""
Redirect non-underscore attribute deletes to dictionary deletes
"""
# the actual code
if name[0] == "_":
return super().__delete__(name)
else:
del self._dictionary[name]
def test():
dictionary = { "a": 1, "b": 2, "c": 3 }
proxy = DictProxy(dictionary)
assert(hasattr(proxy, "a"))
assert(hasattr(proxy, "b"))
assert(hasattr(proxy, "c"))
assert(not hasattr(proxy, "d"))
assert(proxy.a == 1)
assert(proxy.b == 2)
assert(proxy.c == 3)
proxy.a = 4
assert(proxy.a == 4)
assert(dictionary["a"] == 4)
proxy.d = 5
assert(hasattr(proxy, "d"))
assert(proxy.d == 5)
assert("d" in dictionary)
assert(dictionary["d"] == 5)
del proxy.a
assert(not hasattr(proxy, "a"))
assert(not "a" in dictionary)
delattr(proxy, "b")
assert(not hasattr(proxy, "b"))
assert(not "b" in dictionary)
dictionary["a"] = 6
assert(hasattr(proxy, "a"))
assert(proxy.a == 6)
del dictionary["c"]
assert(not hasattr(proxy, "c"))
if __name__ == '__main__':
test()
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