How Do You Prevent Lambda Closure Confusion When Creating Lambdas in Loops?

Preventing Lambda Closure Confusion in Loops

When creating lambdas inside a loop that iterates over a list of objects, it's important to be aware of lambda closure behavior. By default, lambdas capture the variables in the enclosing scope when they are defined. However, if variables change within the loop, lambdas created later in the loop will refer to the updated values.

Consider the following example, where we create lambdas to access an object's some_var attribute:

lambdas_list = []
for obj in obj_list:
    lambdas_list.append(lambda: obj.some_var)

If we then iterate over the lambda list and call each lambda, we may get the same value for all lambdas. This is because the last lambda created in the loop will capture the final state of obj, and that value will be returned by all lambdas.

To solve this, we can specify the object to be captured by the lambda using a default argument. This ensures that each lambda captures the correct object reference:

lambdas_list.append(lambda obj=obj: obj.some_var)

By using this approach, each lambda will capture the object it was intended to refer to when it was created. This will prevent confusion and ensure that the lambdas behave as expected when called later in the loop.

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