CODEWITHSUNDEEP
pythonpython-3.xsum
Phoenix
Phoenix

Reputation: 4646

Python - Sum with Start

>>> sum([1,2,3])
6

Failed attempt to declare start position:

>>> sum([1,2,3],1)
7

Docs say sum(iterable[, start])

Can someone supply me with an example of using sum declaring start position please.

Upvotes: 0

Views: 412

Answers (1)

Paulo Bu
Paulo Bu

Reputation: 29804

That start means the sum starting value, not the position on the array:

sum():

Sums start and the items of an iterable from left to right and returns the total.

If you want to accomplish that you can use list slicing:

>>>sum([1,2,3][1:])
5

This slicing won't work with an iterator, in that case you can use enumerate() in a generator expression. Something like this:

>>> i=iter([1,2,3])
>>> sum(v for i,v in enumerate(i) if i >= 1)
5

Or better yet as pointed out by @lvc on the comments, use the itertools.islice() function to slice the iterator:

>>>import itertools
>>> i=iter([1,2,3])
>>> sum(itertools.islice(i,1,None))
5

Upvotes: 3

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