> For the complete documentation index, see [llms.txt](https://louisazhou.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://louisazhou.gitbook.io/notes/chapter1/list-comprehensions.md).

# List Comprehensions

Say, there is a list, doctor = \['house', 'cuddy', 'chase', 'thirteen', wilson], the list comprehension `[doc[0] for doc in doctor]`  produces the list `['h', 'c', 'c', 't', 'w']`.

### Nested List Comprehension 

```python
matrix = [[col for col in range(5)] for row in range(5)]

#[[0, 1, 2, 3, 4],[0, 1, 2, 3, 4],[0, 1, 2, 3, 4],[0, 1, 2, 3, 4],[0, 1, 2, 3, 4]]

#也可以只打印单独每一行
for row in matrix:
    print(row)          
```

To create the list of lists, you simply have to supply the list comprehension as the **output expression** of the overall list comprehension:

`[`\[*output expression*] `for` *iterator variable* `in` *iterable*`]`

### Conditionals in comprehensions 

new\_nums = \[num + 1 for num in nums]