Note about getattr and '.'

[Carl Banks]

szport at gmail.com wrote:
> There is an interesting skewness in python:
>
> class A(object): pass
>
> >>> a=A()
> >>> setattr(a, '$foo', 17)
> >>> getattr(a, '$foo')
> 17
>
> But I can't write
> >>> a.'$foo'

Likewise, you can write

setattr(a,'hello',17)

but you can't write

a.'hello'

but you can write

a.hello

The only thing that can follow the "." (attribute access) operator is a
valid Python identifier.  Strings may not.  Anyways, it's probably not
a good idea in most cases to use getattr and setattr with a
non-identifier, but Python doesn't prevent you from doing it.  (Which
is good in the occasional case where it is a good idea.)

BTW, Matlab has an interesting syntax; you could have written this:

a.("$foo")

(And because Matlab is weird that way, this was not structure member
access, but some weird hybrid of structure accces and indexing and/or
slicing.  The syntax was very useful in Matlab because there's no
built-in associative array and using this syntax was the easiest way to
get something like it.  In Python we'd do that with a dict, so it's not
so useful here.)


Carl Banks