Python lambda inside range

Question

In the following code I'm supposed to print what is shown in the "should be" portion of the comments in the main method. Not sure how to fix. For example, when the argument is 0 it should print 3 but I get 6. Thank you.

def get_sum_metrics(predictions, metrics=None):
    if metrics is None:
        metrics = []

    for i in range(3):
        metrics.append(lambda x: x + i)

    sum_metrics = 0
    for metric in metrics:
        sum_metrics += metric(predictions)

    return sum_metrics


def main():
    print(get_sum_metrics(0))  # Should be (0 + 0) + (0 + 1) + (0 + 2) = 3
    print(get_sum_metrics(1))  # Should be (1 + 0) + (1 + 1) + (1 + 2) = 6
    print(get_sum_metrics(2))  # Should be (2 + 0) + (2 + 1) + (2 + 2) = 9
    print(get_sum_metrics(3, [lambda x: x]))  # Should be (3) + (3 + 0) + (3 + 1) + (3 + 2) = 15
    print(get_sum_metrics(0))  # Should be (0 + 0) + (0 + 1) + (0 + 2) = 3
    print(get_sum_metrics(1))  # Should be (1 + 0) + (1 + 1) + (1 + 2) = 6
    print(get_sum_metrics(2))  # Should be (2 + 0) + (2 + 1) + (2 + 2) = 9

Sankalpa · Answer 1 · 2020-02-18T13:22:20.643

You have got messed up with the lambda function.The error came because of the free variable assigning error.So,you can replace the code with the following code.

    for i in range(3):
        metrics.append(lambda x,i=i: x + i)

This is the entire code

def get_sum_metrics(predictions, metrics=None):
    if metrics is None:
        metrics = []

    for i in range(3):
        metrics.append(lambda x,i=i: x + i)

    sum_metrics = 0
    for metric in metrics:
        sum_metrics += metric(predictions)

    return sum_metrics


def main():
    print(get_sum_metrics(0))  # Should be (0 + 0) + (0 + 1) + (0 + 2) = 3
    print(get_sum_metrics(1))  # Should be (1 + 0) + (1 + 1) + (1 + 2) = 6
    print(get_sum_metrics(2))  # Should be (2 + 0) + (2 + 1) + (2 + 2) = 9
    print(get_sum_metrics(3, [lambda x: x]))  # Should be (3) + (3 + 0) + (3 + 1) + (3 + 2) = 15
    print(get_sum_metrics(0))  # Should be (0 + 0) + (0 + 1) + (0 + 2) = 3
    print(get_sum_metrics(1))  # Should be (1 + 0) + (1 + 1) + (1 + 2) = 6
    print(get_sum_metrics(2))  # Should be (2 + 0) + (2 + 1) + (2 + 2) = 9

main()

It's better if you refer this thread. It has a full explanation about lambda function.

And if get confused with the relevant theory use this code which is written according to your case that is more simple and easy to understand

def get_sum_metrics(predictions, metrics=None):
    if metrics is None:
        metrics = []



    func=lambda x,i: x + i


    sum_metrics = 0
    for i in range(3):
        sum_metrics += func(predictions,i)

    for metric in metrics:
        sum_metrics+=metric(predictions)
    return sum_metrics


def main():
    print(get_sum_metrics(0))  # Should be (0 + 0) + (0 + 1) + (0 + 2) = 3
    print(get_sum_metrics(1))  # Should be (1 + 0) + (1 + 1) + (1 + 2) = 6
    print(get_sum_metrics(2))  # Should be (2 + 0) + (2 + 1) + (2 + 2) = 9
    print(get_sum_metrics(3, [lambda x: x]))  # Should be (3) + (3 + 0) + (3 + 1) + (3 + 2) = 15
    print(get_sum_metrics(0))  # Should be (0 + 0) + (0 + 1) + (0 + 2) = 3
    print(get_sum_metrics(1))  # Should be (1 + 0) + (1 + 1) + (1 + 2) = 6
    print(get_sum_metrics(2))  # Should be (2 + 0) + (2 + 1) + (2 + 2) = 9

main()

Python lambda inside range

1 Answers1