Question

I’m new in programming so please don’t kill me for asking stupid questions.
I’ve been trying to understand all that class business in Python and I got to the point where could not find answer for my question just by google it.

In my program I need to call a class from within other class based on string returned by function. I found two solutions: one by using getattr() and second one by using globals() / locals().

Decided to go for second solution and got it working but I’m really don’t understand how it’s working.

So there is the code example:

class Test(object):
    def __init__(self):
        print "WORKS!"

room = globals()['Test'] 
room()

type(room()) gives:

<class '__main__.Test'>

type(room) gives:

<type 'type'> # What????

It looks like room() is a class object, but shouldn’t that be room instead of room()?

Please help me because it is a little bit silly if I write a code which I don’t understand myself.

Answer 1

What happens here is the following:

class Test(object):
    def __init__(self):
        print "WORKS!"

room = globals()['Test']

Here you got Test as room the way you wanted. Verify this:

room is Test

should give True.

type(room()) gives:

<class '__main__.Test'>

You do one step an go it backwards: room() returns the same as Test() would – an instance of that class. type() “undoes” this step resp. gets the type of the object – this is, of course, Test.

type(room) gives:

<type 'type'> # What????

Of course – it is the type of a (new style) class. The same as type(Test).

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Be aware, however, that for

In my program I need to call a class from within other class based on string returned by function. I found two solutions: one by using getattr() and second one by using globals() / locals().

it could be better to create an explicitly separate dict. Here you have full control over which objects/classes/… are allowed in that context and which are not.