Make a new list from this Python list of tuples?

Question

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?

Answer 1

选择每个元组的第一个元素：

[t[0] for t in originallist]

Answer 2

Or use the generator form to avoid materializing a list before you need it:

gen = (t[0] for t in originallist)

and when you need the list:

list(gen)