# List of zeros in python

## List of zeros in python

```
#add code here to figure out the number of 0s you need, naming the variable n.
listofzeros = [0] * 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 = [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]
>>>
```

```
$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
```

You should use `[0] * n`

to generate a list with `n`

zeros.

See why [] is faster than list()

There is a gotcha though, both `itertools.repeat`

and `[0] * 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[0].append(1)
a
> [[1], [1], [1], [1], [1], [1], [1], [1], [1], [1]]
```

`[0] * n`

will create the list immediately while `repeat`

can be used to create the list lazily when it is first accessed.

If youre dealing with really large amount of data and your problem doesnt 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.

#### List of zeros in python

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

.

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

So for your loop:

```
for i in range(10):
print [0] * i
```