I'm bringing this discussion over from the python-ideas mailing list to see
what people think. I accidentally discovered that the following works, at least
in Python 3.4.2:
>>> class foo(object):
... pass
...
>>> setattr(foo, '3', 4)
>>> dir(foo)
['3', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__',
'__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__',
'__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__',
'__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__',
'__subclasshook__', '__weakref__']
>>> getattr(foo, '3')
4
>>> bar = foo()
>>> dir(bar)
['3', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__',
'__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__',
'__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__',
'__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__',
'__subclasshook__', '__weakref__']
>>> getattr(bar, '3')
4
>>> hasattr(foo, '3')
True
>>> hasattr(bar, '3')
True
However, the following doesn't work:
>>> foo.3
File "<stdin>", line 1
foo.3
^
SyntaxError: invalid syntax
>>> bar.3
File "<stdin>", line 1
bar.3
^
SyntaxError: invalid syntax
I'd like to suggest that getattr(), setattr(), and hasattr() all be modified so
that syntactically invalid statements raise SyntaxErrors. In messages on
python-ideas, Nick Coghlan mentioned that since a Namespace is just a
dictionary, the normal error raised would be TypeError and not SyntaxError; I'd
like to suggest special-casing this so that using getattr(), setattr(), and
hasattr() in this way raise SyntaxError instead as I think that will be less
astonishing.
Thoughts?
Thanks,
Cem Karan
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