setattr() oddness

Terry Reedy tjreedy at
Fri Jan 15 23:22:42 CET 2010

On 1/15/2010 3:37 PM, Sean DiZazzo wrote:
> Should the following be legal?
>>>> class TEST(object): pass
> ...
>>>> t = TEST()
>>>> setattr(t, "", "123")
>>>> getattr(t, "")
> '123'

Different people have different opinions as to whether setattr (and 
correspondingly getattr) should be strict or permissive as to whether or 
not the 'name' string is a legal name. CPython is permissive. The 
rationale is that checking would take time and prevent possible 
legitimate use cases.

CPython is actually looser than this. Try

t.__dict__[1] = 2

Now there is an 'attribute' whose 'name' is an int! -- and which can 
only be accessed via the same trick of delving into the internals. This 
is, however, implementation behavior that would go away if an 
implementation used string-key-only dicts to store attributes.

Terry Jan Reedy

More information about the Python-list mailing list