# This is the inputlist input_list =[1,0,3,2,0,1,0] and I want output_list as [1,1,2,3,0,0,0] How to solve this?

## Question:

```
input_list =[1,0,3,2,0,1,0]
for a in input_list:
if input_list[a] != 0:
input_list[a] = a
else:
input_list[a] = 0
print(input_list)
```

**Tried this but getting output as input_list =[1,0,3,2,0,1,0]
Instead i want this [1,1,2,3,0,0,0]**

```
for a in input_list:
if input_list[a] != 0:
input_list[a] = a
else:
input_list[a] = 0
print(input_list)
```

## Answers:

You can make a custom sort where you give `0`

infinite weight so it appears at the end of the sorting order.

```
output_list = sorted(input_list, key=lambda x: x if x != 0 else float('inf'))
```

getting output as input_list

No, your code gives `[0, 0, 3, 3, 0, 1, 0]`

, because you use the values as indexes, `for a in input_list`

iterates over values, then you use them `input_list[a]`

as indexes

What you need is sorting, `x or float('inf')`

expression takes `inf`

in case the value of `x`

is 0 (putting it at the end of the list), else it takes the value of `x`

```
input_list = [1, 0, 3, 2, 0, 1, 0]
result = sorted(input_list, key=lambda x: x or float('inf'))
print(result)
```

```
input_list =[1,0,3,2,0,1,0]
input_list.sort()
new_list = [el for el in input_list if el != 0] + [el for el in input_list if el == 0]
```

Output:

```
[1, 1, 2, 3, 0, 0, 0]
```

I think the cleanest way to solve this is:

```
import math
input_list =[1,0,3,2,0,1,0]
input_list = sorted(input_list, key=lambda x: x if x!=0 else math.inf)
```

Which is sorting like one would usually do, but giving the `0`

a weight of `inf`

(infinite) such that it’s always the last item.

There are already some good answers, here is just one more alternative approach, albeit more *concise and little tricky:*

Here it’s use the "True" and "False" of each number and its identity to move all "True" (number is zero) to the end of list.

```
L = [1,0,3,2,0,1,0]
ans = sorted(L, key=lambda x: (x ==0, x))
print(ans)
[1, 1, 2, 3, 0, 0, 0]
```

If you don’t want to create a new list, you can use the same list as this way:

```
L[:] = sorted(L, key=lambda x: (x ==0, x))
```