# [Tutor] Summing arrays

Alan Gauld alan.gauld at yahoo.co.uk
Thu Mar 16 05:12:30 EDT 2017

```On 16/03/17 05:11, Aaliyah Ebrahim wrote:

> def sum2(N):
>
>     b = np.arange(1,N+1,1)
>     mylist = [ ]
>     for i in b:
>         terms = 2*(1+3**(i-1))
>         a = mylist.append[terms]
>     return np.sum(mylist)

> terms = 2*(1+3**(i-1))----> 9         mylist.append[terms]     10
> return np.sum(mylist)     11
> TypeError: 'builtin_function_or_method' object is not subscriptable

You are using [] to call append instead of ().
It should be
a = mylist.append(terms)

However, most of your function could be replaced by
a list comprehension:

def sum2(N):
mylist = [2*(1+3**(i-1)) for i in np.arange(1,N+1,1) ]
return np.sum(mylist)

And I'm not sure the np versions of the functions will
give much advantage over the standard range() and sum()

Any time you see a structure like

aList = []
for <some iteration>
aList.append(<some expression>)

You should consider whether a comprehension would
be more suitable

--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
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http://www.flickr.com/photos/alangauldphotos

```