# List of zeros in python

## Question:

How can I create a `list` which contains only zeros? I want to be able to create a zeros `list` for each `int` in `range(10)`

For example, if the `int` in the range was `4` I will get:

``````[0,0,0,0]
``````

and for `7`:

``````[0,0,0,0,0,0,0]
``````

The easiest way to create a list where all values are the same is multiplying a one-element list by `n`.

``````>>>  * 4
[0, 0, 0, 0]
``````

``````for i in range(10):
print  * i
``````

`zeros=*4`

you can replace `4` in the above example with whatever number you want.

``````zlists = [ * i for i in range(10)]
``````

`zlists` is a list of 0 zeroes, `zlists` is a list of 1 zero, `zlists` is a list of 2 zeroes, etc.

If you want a function which will return an arbitrary number of zeros in a list, try this:

``````def make_zeros(number):
return  * number

list = make_zeros(10)

# list now contains: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
``````

Here is the xrange way:

``````list(0 for i in xrange(0,5))
``````
``````\$ python3
>>> from itertools import repeat
>>> list(repeat(0, 7))
[0, 0, 0, 0, 0, 0, 0]
``````
``````#add code here to figure out the number of 0's you need, naming the variable n.
listofzeros =  * n
``````

if you prefer to put it in the function, just drop in that code and add `return listofzeros`

Which would look like this:

``````def zerolistmaker(n):
listofzeros =  * 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]
>>>
``````
``````\$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(" * 100000", number=1000)
> 0.6624710559844971

timeit('list(itertools.repeat(0, 100000))', 'import itertools', number=1000)
> 1.0820629596710205
``````

You should use ` * n` to generate a list with `n` zeros.

See why [] is faster than list()

There is a gotcha though, both `itertools.repeat` and ` * n` will create lists whose elements refer to same `id`. This is not a problem with immutable objects like integers or strings but if you try to create list of mutable objects like a list of lists (`[[]] * n`) then all the elements will refer to the same object.

``````a = [[]] * 10
a.append(1)
a
> [, , , , , , , , , ]
``````

` * n` will create the list immediately while `repeat` can be used to create the list lazily when it is first accessed.

If you’re dealing with really large amount of data and your problem doesn’t need variable length of list or multiple data types within the list it is better to use `numpy` arrays.

``````timeit('numpy.zeros(100000, numpy.int)', 'import numpy', number=1000)
> 0.057849884033203125
``````

`numpy` arrays will also consume less memory.

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