Discussion on: Narcissistic number

[Pierre Bouillon]

Here is a little implementation in Python3.6:

def is_narcissistic(nb: int) -> bool:
    return nb == sum([int(c)**len(str(nb)) for c in str(nb)])


if __name__ == '__main__':
    print([nb for nb in range(10000) if is_narcissistic(nb)])

Display:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 153, 370, 371, 407, 1634, 8208, 9474]

[Tata Ganesh]

Awesome answer, Pierre!
I have one doubt though. Wouldn't it be better to first convert nb into a string, and then just pass the string to the list comprehension, instead of doing str(nb) for every iteration? That is,

str_nb = str(nb)
return nb == sum(int(c)**len(str_nb) for c in str_nb)

This might be a little more efficient. Also, we can remove the list comprehension inside and replace it with a generator.

[Pierre Bouillon]

Yeah you're right! Thank you, that's clever!

[Paul van der Sluis]

This is fun! Here is a Python 3.5 one-liner with only one calculation of the length of nb per nb :

print([nb for nb in range(10000) if nb == sum(int(c)**l for l in [len(str(nb))] for c in str(nb))])

And now with also one conversion of str(nb) per nb:

print([nb for nb in range(10000) if nb == sum(int(c)**l for str_nb in [str(nb)] for l in [len(str_nb)] for c in str_nb)])