I am trying to define a list of lists with a loop in Python. I want to construct the following list:
x=[[0,0],[1,0],[2,0],...,[9,0]]
Here is basically what I do:
x=[[0,0]]*10
for i in range(10):
x[i][0]=i
print x
However, I end up with the following list:
x=[[9,0],[9,0],[9,0],...,[9,0]]
What am I doing wrong? Thank you so much for your help
Is this what you are trying to do?
>>> [[i, 0] for i in range(10)]
[[0, 0], [1, 0], [2, 0], [3, 0], [4, 0], [5, 0], [6, 0], [7, 0], [8, 0], [9, 0]]
What was wrong with that you were doing is that you were creating a list, and then by using the * you were not creating more, you were just making more references to it, this means that each time you changed the list, you were changing the same list each time.
>>> a = [[]]*10
>>> a
[[], [], [], [], [], [], [], [], [], []]
>>> a[0].append('X')
>>> a
[['X'], ['X'], ['X'], ['X'], ['X'], ['X'], ['X'], ['X'], ['X'], ['X']]
When you do
x=[[0,0]]*10
you are not creating 10 different elements, but simply copying the reference to the same element 10 times. What you actually need is
x=[[i,0] for i in range(10)]
use this,
a=[[0,i] for i in range(10)]
print a
output is like:
[[0, 0], [0, 1], [0, 2], [0, 3], [0, 4], [0, 5], [0, 6], [0, 7], [0, 8], [0, 9]]
