A more pythonic way to build a class based on a string (how not to use eval)

Question

OK.

So I've got a database where I want to store references to other Python objects (right now I'm using to store inventory information for person stores of beer recipe ingredients).

Since there are about 15-20 different categories of ingredients (all represented by individual SQLObjects) I don't want to do a bunch of RelatedJoin columns since, well, I'm lazy, and it seems like it's not the "best" or "pythonic" solution as it is.

So right now I'm doing this:

class Inventory(SQLObject):
    inventory_item_id = IntCol(default=0)
    amount = DecimalCol(size=6, precision=2, default=0)
    amount_units = IntCol(default=Measure.GM)
    purchased_on = DateCol(default=datetime.now())
    purchased_from = UnicodeCol(default=None, length=256)
    price = CurrencyCol(default=0)
    notes = UnicodeCol(default=None)
    inventory_type = UnicodeCol(default=None)

    def _get_name(self):
        return eval(self.inventory_type).get(self.inventory_item_id).name

    def _set_inventory_item_id(self, value):
        self.inventory_type = value.__class__.__name__
        self._SO_set_inventory_item_id(value.id)

Please note the ICKY eval() in the _get_name() method.

How would I go about calling the SQLObject class referenced by the string I'm getting from __class__.__name__ without using eval()? Or is this an appropriate place to utilize eval()? (I'm sort of of the mindset where it's never appropriate to use eval() -- however since the system never uses any end user input in the eval() it seems "safe".)

couldn't this usage of eval be replaced with globals()[self.inventory_type]? — Dan D.
– Dan D., Commented Dec 12, 2011 at 0:44
eval(self.inventory_type) is an imported class object (a subclass of the SQLObject class), not a variable. doesn't globals() only show declared variables? And SQLObject.get is not a @classmethod — tkone
– tkone, Commented Dec 12, 2011 at 1:05
if you import a module its name or the names imported appears in the return value of globals(). >>> import os / >>> 'os' in globals() / True — Dan D.
– Dan D., Commented Dec 12, 2011 at 1:14
oh crap. You're right. If you make this an answer I'll accept it! — tkone
– tkone, Commented Dec 12, 2011 at 1:32

Dan D. · Accepted Answer · 2011-12-12 01:39:23Z

3

To get the value of a global by name; Use:

globals()[self.inventory_type]

answered Dec 12, 2011 at 1:39

Dan D.

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A more pythonic way to build a class based on a string (how not to use eval)

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