Why is there difference between cmd line and .py file?

[Steven D'Aprano]

On Wednesday 06 January 2016 07:37, John Gordon wrote:

> The built-in function sum() returns a single value, not a list, so this
> is a reasonable error.

Not quite. It depends on what arguments you give it.

py> a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
py> sum(a, [])
[1, 2, 3, 4, 5, 6, 7, 8, 9]


But your point is well taken. In this case, the call:

sum(expectation_A)

defaults to an initial value of 0, so expectation_A almost certainly is a 
list of numbers, in which case sum will return a single number, not a list 
or array.

-- 
Steve