Run different class based on variable name?

Question

Let's say we have a few different classes: ClassA, ClassB, ClassC, and ClassD. I have a variable I will set based on different circumstances. I know what it will be ahead of time, but I don't want to have to rewrite many different lines of code in different files each time I need to change it. It is NOT user set.

So now we have Variable = ClassX

So, Let's say I set Variable to ClassA. How can I make it call ClassA using just that? For example, I know I can do this:

Variable = ClassA
if Variable == ClassA:
     # Call ClassA and run it
elif Variable == ClassB:
     # Call ClassB and run it
elif Variable == ClassC:
     # Call ClassC and run it
elif Variable == ClassD:
     # Call ClassD and run it

However, I want to do something like this:

Variable = ClassA
V = Variable()

Is this possible?

EDIT: A little more detail...

So I have 3 files that are used in this scenario.

File1.py:

# Class = ClassA
# Class = ClassB
Class = ClassC
# Class = ClassD
...
if Class == "ClassA":
    c = ClassSystem.ClassA
    short_name = c.get_short_name()
elif Class == "ClassB":
    c = ClassSystem.ClassB
    short_name = c.get_short_name()
elif Class == "ClassC":
    c = ClassSystem.ClassC
    short_name = c.get_short_name()
elif Class == "ClassD":
    c = ClassSystem.ClassD
    short_name = c.get_short_name()
...

File2.py:

from Folder.File1 import short_name
from Folder.ClassSystem import *
...
S = short_name()
S.get_information()

This doesn't seem to work. File2 is referencing the variable from file1. I then need File2 to use the variable from File1 to run the same class in ClassSystem.

Check this out https://stackoverflow.com/questions/2225038/determine-the-type-of-an-object — VTodorov, Dec 04 '17 at 12:17
@NilsWerner I have added more information. It doesn't seem to work in this scenario. — Cody Dostal, Dec 04 '17 at 12:35

score 2 · Accepted Answer · answered Dec 04 '17 at 12:18

Yes, completely possible. Instead of doing it with ifs though, the most compact approach would include a dictionary of class names to class objects.

You can then key the dictionary and call the resulting class:

cls_dict = {c.__name__: c for c in {ClassA, ClassB}}
v = 'ClassA'
cls_dict[v]()

the set of classes can, of course, be altered to include any additional objects you wish.

score 1 · Answer 2 · answered Dec 04 '17 at 12:36

1

You can use eval,

c_name = 'ClassA'
obj = eval(c_name)()

but i am not sure if eval is the recommended way to do this.

answered Dec 04 '17 at 12:36

Manjunath

150
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Run different class based on variable name?

2 Answers2