Raymond Hettinger <[email protected]> added the comment:
I don't think we can mark this as an implementation detail for setattr(). The
details are downstream and determined by the target object, not by setattr()
itself.
Suggested wording:
'''
Note, setattr() attempts to update the object with the given attr/value pair.
Whether this succeeds and what its affect is is determined by the target object.
If an object's class defines `__slots__`, the attribute may not be writeable.
If an object's class defines property with a setter method, the *setattr()*
will trigger the setter method which may or may not actually write the
attribute.
For objects that have a regular dictionary (which is the typical case), the
*setattr()* call can make any string keyed update allowed by the dictionary
including keys that aren't valid identifiers -- for example setattr(a, '1',
'one')
will be the equivalent of vars()['1'] ='one'.
This issue has little to do with setattr() and is more related to the fact that
instance dictionaries can hold any valid key. In a way, it is no different than
a user writing a.__dict__['1'] = 'one'. That has always been allowed and the
__dict__ attribute is documented as writeable, so a user is also allowed to
write `a.dict = {'1': 'one'}.
'''
In short, we can talk about this in the setattr() docs but it isn't really a
setattr() issue. Also, the behavior is effectively guaranteed by the other
things users are allowed to do, so there is no merit in marking this as an
implementation detail. Non-identifier keys can make it into an instance
dictionary via multiple paths that are guaranteed to work.
----------
nosy: +rhettinger
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<https://bugs.python.org/issue35105>
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