Dynamically substitute variables into arguments in python

Question

In python, I'm trying to come up with a good way to add a variable that dynamically replicates the primary object every time it encounters a Variable class as one of the inputs. So if the variable class has 2 different input values, it will create 2 objects. For example:

objects = Object(arg1=10, arg2=Variable([10, 20]))

output:

objects = [Object(arg1=10, arg2=10), Object(arg1=10, arg2=20)]

The tricky part is that the Variable class could be any input for any sub-object, too. For example

objects = Object(subobject1=Subobject(arg1=Variable([10, 20]))

output:

objects = [Object(subobject1=Subobject(arg1=10)), Object(subobject1=Subobject(arg1=20))]

This is for a Blockly project, which is a visual programming language that generates python code from blocks. In that format, its sometimes more natural to use a variable as an input instead of wrapping all of the code in a loop. That's the reason why I'm trying to awkwardly inject a variable into the middle of a section of code instead of just doing a loop.

chepner · Accepted Answer · 2021-08-14 20:15:08Z

2

You're expecting far too much work to be done inside Object.__new__ or Object.__init__, as it would appear that arguments used to create one of its arguments should be taken into consideration.

Be explicit, and use a list comprehension to state what you mean.

objects = [Object(arg1=10, arg2=x) for x in [10, 20]]

or

objects = [Object(subobject=Subobject(arg1=x)) for x in [10, 20]]

If you want some other construct in Blockly, that's a problem to solve in Blockly, not in Python.

answered Aug 14, 2021 at 20:15

chepner

538k77 gold badges594 silver badges746 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Troy D Over a year ago

I wouldn't know ahead of time whether arg2=10, or arg2=Variable([10, 20]), or arg2=Variable([Object1, Object2]), so I couldn't just create the objects in a predefined loop. I won't know ahead of time what the users will want to enter as variables, or which inputs will be Variables. Also, the Variable could be any one of 20 or more different inputs, and I have to keep track of them all somehow, so having every input as a looped over list would be pretty messy, I think. I think I'm looking for something like a director or constructor class that finds Variable objects and then constructs.

chepner Over a year ago

That's part of your problem. Object doesn't and shouldn't know about what argument is being passed to Subobject. At best, it can get information from the subobject argument that the Subobject explicitly makes available, and maybe use that to make a decision about what to return, but you appear to be trying to have your code make decisions that the caller should be making.

Collectives™ on Stack Overflow

Dynamically substitute variables into arguments in python

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related