CODEWITHSUNDEEP
pythonfunction
eagertoLearn
eagertoLearn

Reputation: 10142

how to write this function in more concise manner in python

The beauty of python is often reflected in its simplicity and one-liner codes. I am slowly getting myself in writing them. I have a function that calculates the sum of n powers of 2.

ex: if n==4, I get 2^4+2^3+2^2+2^1+2^0 I have this function which works fine, but wondering if there is room for condensing to one or two lines

>>> def sumpowers(n):
...    sum=0
...    for x in range(n+1):
...       sum+=pow(2,x)
...    return sum
... 
>>> sumpowers(31)
4294967295

Any tips or some use of built-ins that can improve it in terms of simplicity?

Thanks

Upvotes: 2

Views: 166

Answers (5)

brain storm
brain storm

Reputation: 31252

using reduce built-in and lambda, you could achieve it:

>>> reduce(lambda x,y: x+y, [pow(2,i) for i in range(32)])
4294967295

in terms of function:
try this:
    >>> def test(n):
...    return reduce(lambda x,y: x+y,[pow(2,i) for i in range(n+1)])
... 
>>> test(31)
4294967295

EDIT: using reduce is absolutely not necessary. as pointed out in the comments, it might not often be a good idea. but it is an aspect of functional programming that could be made of use and is one of several ways pointed out

Upvotes: 0

Óscar López
Óscar López

Reputation: 236004

Try this solution, is more idiomatic:

def sumpowers(n):
    return sum(2**x for x in range(n+1))

The "trick" to make it more concise lies in using the following:

  • A generator expression, instead of explicit looping
  • The sum built-in function, instead of a counter variable
  • The ** operator, instead of the pow built-in function (the two are equivalent when using two arguments)

But wait! we can make things even simpler by using mathematical properties. The function is equivalent to this (with kudos to @fp for pointing it out first):

def sumpowers(n):
    return 2**(n+1)-1

Either way, it works as expected:

sumpowers(31)
=> 4294967295

Upvotes: 2

Jack_of_All_Trades
Jack_of_All_Trades

Reputation: 11468

Nothing is better in this case than list comprehension.

my_sum=sum([2**x for x in range(n+1)])

Upvotes: 2

user2555451
user2555451

Reputation:

That for-loop can be replaced with the sum built-in and a generator expression:

>>> def sumpowers(n):
...     return sum(pow(2,x) for x in range(n+1))
...
>>> sumpowers(31)
4294967295
>>>

You may also want to replace pow(2,x) with just 2**x:

>>> def sumpowers(n):
...     return sum(2**x for x in range(n+1))
...
>>> sumpowers(31)
4294967295
>>>

Upvotes: 3

John Percival Hackworth
John Percival Hackworth

Reputation: 11531

Try the following:

def sumpowers(n):
    return ((2 ** (n+1)) - 1)

Upvotes: 3

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