Python Beginners: Creating dynamic class objects with dynamic attributes with loops

Question

I'm trying to create some simple objects that are defined dynamically through a class - to allow me to rapidly iterate through the creation of all possibilities of these objects.

class NSObjects:
    def __init__(self, shape, position, shading):
        self.shape = shape
        self.position = position
        self.shading = shading

    def __str__(self):
        return '{} - {} - {}'.format(self.shape(), self.position(), self.shading())


def NSGenerator_1():
    for i in range (0,3):
        obj_1_i = NSObjects(shape_init_top + i, posn_init_top+i, shading_init_top+i)

    for i in range (3,6):
        obj_1_i = NSObjects(shape_init_mid + i, posn_init_mid+i, shading_init_mid+i)

    for i in range (6,9):
        obj_1_i = NSObjects(shape_init_mid + i, posn_init_mid+i, shading_init_mid+i)

NSGenerator_1()
print(obj_1_2)

At the moment it is telling me that obj_1_2 doesn't exist. For the purpose of this you can assume that I have defined all the init variables to start at 0, 1 or 2 elsewhere in the code. I am basically trying to create a series of objects which will have properties as defined by a mathematical formula.

Thanks in advance for any help you can provide (I only started coding a few weeks ago so this might be a very silly question!)

gilch · Accepted Answer · 2018-12-29 06:53:17Z

2

You only ever assigned to obj_1_i, not obj_1_2, and it was local to the function. There is no way for Python to tell that the _i was meant as a separate variable instead of part of the longer variable name. For a quick fix, try replacing the obj_1_i = parts with globals()[f'obj_1_{i}'] =.

But rolling numeric indexes into the variable names like that (_1_2) is a code smell. A better design is to actually use them as indexes to a data structure, like a list or dict.

For example, define obj = {} at the top level (outside of any class or function).

Then you can replace obj_1_2 everywhere with obj[1, 2], etc. If you wrote them that way,
obj[1, i] would work as you expect inside those for loops.

edited Dec 29, 2018 at 6:53

answered Dec 29, 2018 at 6:41

gilch

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1 Comment

tichy255 Over a year ago

Thanks! This makes perfect sense - I need all the style tips I can get!

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