Map and lambda function

Question

I'm currently doing a hackerrank problem.

The objective is to find the cubes of the first n Fibonacci numbers. The user inputs n. So for example, if the user inputs 5, the output should be [0, 1, 1, 8, 27], since the first five Fibonacci numbers are [0, 1, 1, 2, 3].

I've written the following code:

cube = lambda x: x**3 # complete the lambda function 

def fibonacci(n):
    # return a list of fibonacci numbers
    initiallist = []
    for i in range(n):
        if i < 2:
            initiallist += [i]          
        else:
            initiallist += [initiallist[-1] + initiallist[-2]]
    return initiallist

I'm given the following code (which I cannot edit):

if __name__ == '__main__':
    n = int(input())
    print(map(cube, fibonacci(n)))

The problem is that my code fails the test cases because it returns a map object instead of a list. How can I ensure it returns a list instead?

if you can't change code in __main__ then you can only use Python 2 instead of Python 3 to get correct result. (or maybe overwrite function map) — furas
– furas, Commented Jan 21, 2017 at 22:55
In Python 2 the map function returns a list instead of a map object, so this should work as is. — Ewoud
– Ewoud, Commented Jan 21, 2017 at 23:01

Simeon Aleksov · Accepted Answer · 2017-01-21 23:06:40Z

4

Just add list(),

if __name__ == '__main__':
    n = int(input())
    print(list(map(cube, fibonacci(n))))

I undeleted my comment because this is the is solution to map object, I don't think you can modify it before you actually called. as Ewoud said, map function acts differently in python3 and python2.

edited Jan 21, 2017 at 23:06

answered Jan 21, 2017 at 22:53

Simeon Aleksov

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Comments

Ewoud · Accepted Answer · 2017-01-21 22:57:40Z

2

You can just put list(...) around it, so

print(list(map(cube, fibonacci(n))))

(I havent tested the rest of your code)

Edit: If you are not to change the main function you either have to change the print or map function or use python 2.

edited Jan 21, 2017 at 22:57

answered Jan 21, 2017 at 22:53

Ewoud

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1 Comment

kingstante Over a year ago

Once again, the user can not edit that line of code.

Maggie · Accepted Answer · 2017-01-22 08:14:13Z

1

If you can't edit the main function then use Python2.X instead of Python3.x. In Python3.x, map() function return iterator.

Here's [a link] https://docs.python.org/3/library/functions.html#map

answered Jan 22, 2017 at 8:14

Maggie

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Mark Vassell · Accepted Answer · 2017-06-09 05:29:55Z

This should give you more than you need. I added a few extra bits like looping and input validation just in case. Hope this helps

General Formula F(n) = F(n-1) + F(n-2)

Get User input

    def get_user_input():
        while True:
            try:
                nums_in_list = int(input("Enter the amout of numbers you want in the fibonacci list: "))

                if nums_in_list < 1:
                    print("Please enter a number greater than 0.")
                    continue

                return nums_in_list

            except ValueError:
                print ("Please enter an integer.")

Create Fabonacci List based on user input

    def genterate_list(user_input):
        fab_list = [0]
        if user_input == 1:
            return fab_list
        elif user_input == 2:
            fab_list.append(1)
            return fab_list
        else:
            count = 1
            while user_input > count:
                if count == 2:
                    fab_list.append(1)
                elif count > 2:
                    fab_list.append(fab_list[count - 2] + fab_list[count - 3])

                count += 1
        return fab_list

Extra Add in to loop the program

def loop_program():
    while True:
        opts = ['y', 'Y', 'N', 'n']

        loop = input("Would you like to run the program again (y/n): ")

        if loop not in opts:
            print("Please select (y/n): ")
            continue
        elif loop == 'N' or loop == 'n':
            return "N"
        else:
            return "Y"

Main section: Calls the functions defined above Displays the outputs.

    if __name__ == '__main__':
        while True:
            original = genterate_list(get_user_input())
            print("Original Fabonacci")

            for x in original:
                print(x)

            cube_funtion = lambda value : value ** 3
            cube_result = map(cube_funtion, original)
            print("Cubed Values")
            list(map(print, cube_result))
            if loop_program() == "N":
                break

DoesEatOats · Accepted Answer · 2019-05-23 11:36:16Z

0

I just ran this and it worked successfully on hackerank { cube = lambda x: x**3 # complete the lambda function

def fibonacci(n):
# return a list of fibonacci numbers
initiallist = []
for i in range(n):
    if i < 2:
        initiallist += [i]          
    else:
        initiallist += [initiallist[-1] + initiallist[-2]]
return initiallist

if __name__ == '__main__':
n = int(input())
print(list(map(cube, fibonacci(n))))

}

answered May 23, 2019 at 11:36

DoesEatOats

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