Python - Access object attributes as in a dictionary

Question

>>> my_object.name = 'stuff'
>>> my_str = 'name'
>>> my_object[my_str] # won't work because it's not a dictionary :)

How can I access to the fields of my_object defined on my_str ?

Solution 1

getattr(my_object, my_str)

Or, if you're not sure if the name exists as a key and want to provide a fallback instead of throwing an exception:

getattr(my_object, my_str, "Could not find anything")

More on getattr.

Solution 2

You can provide support for the [] operator for objects of your class by defining a small family of methods - getitem and setitem, principally. See the next few entries in the docs for some others to implement, for full support.

Comments

[Admin]

Note that this breaks for properties, __slots__ and __getattr__/__getattribute__/__setattr__ overloads - and probably some other things.

[Pierre de LESPINAY]

What is the advantage against myobject.__dict__[my_str] ? better performance ?

[Pierre de LESPINAY]

Ok thank you for the info. Do you think getattr(my_object, my_str) is better for performance also ?

[Admin]

Performance is your least concern here. If it is, you could rewrite that part (i.e. the whole loop, to avoid many cross-language calls) in C, but you should have solid proof of an unacceptable slowdown before considering such optimizations.

[Tom]

Can I fall back on the standard "It's more Pythonic" answer? Also, tapping into the private __ variables comes with its own set of risks. What you're trying to do is what getattr and setattr are for.

[oriadam]

Word of warning though - if you use dynamic attribute names you should either use try: or add if hasattr( before using getattr to make sure you're not trying to access something that's not there.

[Tom]

Huh? getattr does not throw an exception if the attribute doesn't exist. It's basically syntactic sugar for if hasattr give me that else give me the default.

[Tom]

To answer my own ignorance down the road that's because I was always passing a third argument for the default, e.g., getattr(my_object, my_str, None).

[E. Zeytinci]

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