How to instantiate a class given its name as a string?

Question

Give some class definitiona in python, e.g.

class A(object):
    def __init__(self):
        self.x = 5

class B(object):
    def __init(self):
        self.x = 42

I want to instantiate one of these classes given its name as string. So for example, if classname is A, then I want to do something like

myinstance = SOMETHING(classname)

which should correspond to

myinstance = A()

Is there a way to do this without the use of eval eval or maps? If not, I would do the following:

map = {'A': A, 'B': B}
myinstance = map[classname]()

@dano: Its not about calling a class method by a name given in a string. — Alex, Aug 11 '14 at 18:53
@Alex: no, it is about calling a class given a name in a string. But to Python, there is no difference between a class and a function. — Martijn Pieters, Aug 11 '14 at 18:54
@Alex Just do exactly what the top two answers in that question say, but pass your class' name instead of a function name. — dano, Aug 11 '14 at 18:55
@all: I see, then this is probably a duplicate. If Martin says so, it must be.... — Alex, Aug 11 '14 at 18:56

score 0 · Answer 1 · answered Aug 11 '14 at 18:56

Considering that the Python naming scheme is based on maps, you will be using maps of one sort or another even if you use eval.

Building your own map is the most appropriate, but you can also use globals() or retrieve it from a module if your classes are stored somewhere else:

import util_module
getattr(util_module, 'A') ()

How to instantiate a class given its name as a string?

1 Answers1