Problem
How can I make a list that only contains zeros? I’d like to be able to generate a zeros list for each integer in the range (10)
For example, if the range’s int was 4, I’d get:
[0,0,0,0]
and for 7:
[0,0,0,0,0,0,0]
Asked by user1040563
Solution #1
#add code here to figure out the number of 0's you need, naming the variable n.
listofzeros = [0] * n
If you’d rather put it in a function, simply paste that code in and add return listofzeros.
This is what it would look like:
def zerolistmaker(n):
listofzeros = [0] * n
return listofzeros
sample output:
>>> zerolistmaker(4)
[0, 0, 0, 0]
>>> zerolistmaker(5)
[0, 0, 0, 0, 0]
>>> zerolistmaker(15)
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
>>>
Answered by Tiffany
Solution #2
$python 2.7.8
from timeit import timeit
import numpy
timeit("list(0 for i in xrange(0, 100000))", number=1000)
> 8.173301935195923
timeit("[0 for i in xrange(0, 100000)]", number=1000)
> 4.881675958633423
timeit("[0] * 100000", number=1000)
> 0.6624710559844971
timeit('list(itertools.repeat(0, 100000))', 'import itertools', number=1000)
> 1.0820629596710205
To make a list containing n zeros, you should use [0] * n.
See why [] is more efficient than a list ()
However, both itertools have a catch. repeat and [0] * n will generate lists with the same id as the elements. This is not a problem with immutable things such as integers or strings, but if you try to make a list of changeable objects, such as a list of lists ([[]] * n), all of the items will refer to the same object.
a = [[]] * 10
a[0].append(1)
a
> [[1], [1], [1], [1], [1], [1], [1], [1], [1], [1]]
[0] * n creates the list instantaneously, whereas repeat creates the list slowly when it is accessed for the first time.
Numpy arrays are superior if you’re dealing with a lot of data and your problem doesn’t require changeable list lengths or multiple data types within the list.
timeit('numpy.zeros(100000, numpy.int)', 'import numpy', number=1000)
> 0.057849884033203125
In addition, numpy arrays will use less RAM.
Answered by Seppo Erviälä
Solution #3
Multiplying a one-element list by n is the simplest approach to make a list with all the same values.
>>> [0] * 4
[0, 0, 0, 0]
So here’s the deal with your loop:
for i in range(10):
print [0] * i
Answered by Andrew Clark
Solution #4
$ python3
>>> from itertools import repeat
>>> list(repeat(0, 7))
[0, 0, 0, 0, 0, 0, 0]
Answered by kev
Solution #5
zlists = [[0] * i for i in range(10)]
zlists[0] contains 0 zeroes, zlists[1] contains 1 zero, zlists[2] contains 2 zeroes, and so on.
Answered by kindall
Post is based on https://stackoverflow.com/questions/8528178/list-of-zeros-in-python