1

setattr allows you to dynamically name attributes in Python classes. I'm trying to do something similar with an App Engine Model: 

class MyModel(db.Model):
    def __init__(self, *args, **kwargs):
        super(MyModel, self).__init__(*args, **kwargs)

        # Doesn't fully work
        setatr(self, 'prop1', db.ListProperty(db.Key))
        setatr(self, 'prop2', db.StringListProperty())

    # Works fully
    # prop1 = db.ListProperty(db.Key))
    # prop2 = db.StringListProperty())

This code compiles, but when I call model.prop1.append(key) later on, I get this error: 

AttributeError: 'ListProperty' object has no attribute 'append'

I suspect this is because prop1 is declared in models instead of self.prop1, but I don't fully understand the syntax's significance.

Has anyone accomplished this, or does anyone have any insight into syntactic differences?

Matt Norris
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3 Answers3

5

I think you're looking for the db.Expando class (instead of db.Model).

David Underhill
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1

This SO question:

gives an example of what you want to do.

Community
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icyrock.com
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1

Not sure but would this work maybe:

class MyModel(db.Model):
    @classmethod
    def new(cls, *args, **kwargs):        
        setattr(cls, 'props1', db.ListProperty(db.Key))
        setattr(cls, 'props2', db.StringListProperty())
        mymodel = cls(*args, **kwargs)
        delattr(cls, 'props1')
        delattr(cls, 'props2')
        return mymodel
Josh
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