python sum function forloop

Question

I am just wondering.. How can I sum over different elements in a for loop?

for element in [(2,7),(9,11)] :
        g=sum(element[1]-element[0]+1)
        print g

If I remove 'sum', I get:

6
3

Answer 1

I'm not sure what you do want to get. Is it this?

>>> print sum(element[1]-element[0]+1 for element in [(2,7), (9,11)])
9

This generator expression is equivalent to

temp = []
for element in [(2,7), (9,11)]:
    temp.append(element[1]-element[0]+1)
print sum(temp)

but it avoids building a list in memory and is therefore more efficient.

Answer 2

You could replace this with a generator expression:

In [20]: sum(element[1] - element[0] + 1 for element in [(2, 7), (9, 11)])
Out[20]: 9

This could be simplified to:

In [21]: sum(y - x + 1 for x,y in [(2, 7), (9, 11)])
Out[21]: 9

...which I find easier to read and guarantees that each element in the list has exactly two elements. And it doesn't use unnecessary lambdas.