partial sums problem

Ian Kelly ian.g.kelly at gmail.com
Wed Sep 29 01:52:36 CEST 2010


On Tue, Sep 28, 2010 at 4:57 PM, kj <no.email at please.post> wrote:

>
>
> The following attempt to get a list of partial sums fails:
>
> >>> s = 0
> >>> [((s += t) and s) for t in range(1, 10)]
>  File "<stdin>", line 1
>    [((s += t) and s) for t in range(1, 10)]
>          ^
> SyntaxError: invalid syntax
>

Because in Python assignment is a statement, not an expression.

What's the best way to get a list of partial sums?
>

sum = 0
sums = []
for t in range(1, 10):
    sum += t
    sums.append(sum)

Or, if you prefer to keep it functional in nature:

def append_sum(sums, x):
    return sums + [(sums[-1] if sums else 0) + x]

reduce(append_sum, range(1, 10), [])

Cheers,
Ian
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