Python - How to call an instance from a given string?

Question

I want to call the function bar() from the instance foo, just like this:

foo.bar()

But both instance and function names come from a given string. I tried getattr but it just let me use a string for the function, not the instance:

strbar = 'bar'    
getattr(foo, strbar)()

What I want to do is something like:

strfoo = 'foo'
strbar = 'bar'
getattr(strfoo, strbar)()

But it gives me:

AttributeError: 'str' object has no attribute 'bar'

I know a dictionary could be an option, but that makes me write a really long dictionary.

tuxtimo · Accepted Answer · 2015-10-28 00:05:02Z

4

The best way would be to have a dictionary or a similar structure. However you could use eval which is evil. Or you can get your instance from the locals() dictionary:

getattr(locals()[instance_name], attribute_name)

I would think about redesigning your code. There must be a better solution as eval or locals ... like a dictionary ...

answered Oct 28, 2015 at 0:05

tuxtimo

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6 Comments

Kevin Over a year ago

Yes, eval() is potentially very dangerous if you're not careful about where you got that string and who can control its contents.

inbinder Over a year ago

I'm confused at what's the user's trying do to here? Can anyone offer another example of doing this with a different approach to the code?

tuxtimo Over a year ago

didn't get the first one but for a different approach we, or at least I, need some more information about what he's trying to do ..

Xesa Over a year ago

Using the locals dictionary is exactly what I needed. But I read in a lot of places that using this is dangerous. Could you explain me why?

tuxtimo Over a year ago

Especially writing to it can be very dangerous and is not reliable. However, reading from it is considered bad practice because you can just read anything in the local scope and not just the values you wanted to...

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