A sequence of empty lists of length n in Python?

Question

In python `[]*2`, gives `[]` What is the simplest way to get `[[],[]]` instead?

Accepted Answer

You probably want:

```
[[] for _ in range(n)]
```

Unlike `[[]] * n`, this will give you unique inner lists (appending to one doesn't append to them all). e.g.:

```
>>> x = [[] for _ in range(n)]
>>> x[0].append(1) 
>>> x
[[1], [], []]
```

compared to:

```
>>> x = [[]] * 3
>>> x[0].append(1)
>>> x
[[1], [1], [1]]
```

Note that this latter idiom (`[[]] * n`) is a very common mistake that crops up around here in different contexts pretty frequently.

Solution