CODEWITHSUNDEEP
python-3.x
BiGYaN
BiGYaN

Reputation: 7159

When to use list with sum in python

Here are two examples:

sum(list(map(lambda x:x,range(10))))

and

sum(range(10))

The second example does not require a list(), but the first one does. Why?

How do I know when is list() a necessity? Similarly using list() for min() and max().

I am running python 3.3.5 with ipython 2.2.0. Here is what I see: enter image description here

print(sum) results in <built-in function sum> from python console and <function sum at 0x7f965257eb00> from ipythonNotebook. Looks like an issue with hidden imports in notebook.

Upvotes: 0

Views: 164

Answers (2)

shx2
shx2

Reputation: 64328

Neither of the examples require the use of list. The sum builtin function works with any iterable, so converting the result of map to a list isn't necessary.

Just in case, make sure you are indeed using the builtin sum function. Doing something like from numpy import * would override that. (you can simply print sum and see what you get).

Upvotes: 3

JCm
JCm

Reputation: 1999

I guess the 1st one just enforces and expects the output of the map function to be a list because if there are multiple arguments, map() returns a list consisting of tuples containing the corresponding items from all iterables.

But either way base on your example, it would still work.

Upvotes: 1

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