Q:

Make a new list from this Python list of tuples?

The dimensions of an a4 piece of paper are 8.5x11 inches, and the number of pixels which can fit inside these inches increases with dots per inch.
I made a Python list of tuples which expresses this as, using
>>> [(i,8.5*i,11*i) for i in range(18)]

which gives
[(0, 0.0, 0), (1, 8.5, 11), (2, 17.0, 22), (3, 25.5, 33), (4, 34.0, 44), (5, 42.5, 55), (6, 51.0, 66), (7, 59.5, 77), (8, 68.0, 88), (9, 76.5, 99), (10, 85.0, 110), (11, 93.5, 121), (12, 102.0, 132), (13, 110.5, 143), (14, 119.0, 154), (15, 127.5, 165), (16, 136.0, 176), (17, 144.5, 187)]

I then want to make a new list that contains only the factor by which the quantities in the first list grow, namely the sequence {0..18}.
But I want to do this by performing some operation on the first list. How can I do it?

A:

Select the first element of each tuple:
[t[0] for t in originallist]

