python - how to create a list of lists

Question

My Python code generates a list everytime it loops:

list = np.genfromtxt('temp.txt', usecols=3, dtype=[('floatname','float')], skip_header=1)

But I want to save each one - I need a list of lists right?

So I tried:

list[i] = np.genfromtxt('temp.txt', usecols=3, dtype=[('floatname','float')], skip_header=1)

But Python now tells me that "list" is not defined. I'm not sure how I go about defining it. Also, is a list of lists the same as an array??

Thank you!

Answer 1

You want to create an empty list, then append the created list to it. This will give you the list of lists. Example:

>>> l = []
>>> l.append([1,2,3])
>>> l.append([4,5,6])
>>> l
[[1, 2, 3], [4, 5, 6]]