Python hacks

Question 1

Simple tying example for addition function

Answer 1

def add(a: int, b: int) -> int:
return a+b

Question 2

Iterate through list with indices

Answer 2

for i, x in enumerate(list_ab):

Question 3

Iterate through multiple iterables in parallel

Answer 3

a = [1, 2, 3]
b = [10, 20, 30]
for x, y in zip(a, b):
    print(x + y)   

Question 4

Dictionary that adds keys if they are not included

Answer 4

```
from collections import defaultdict
counts = defaultdict(int)
for ch in “banana”:
counts[ch] += 1
~~~

Question 5

What should you be careful about when iterating over a list?

Answer 5

Changing the list while iterating it will also change the iteration, instead iterate over a copy

Question 6

Create a defaultdict with values

Answer 6

from collections import defaultdict
d = {"a": [1, 2], "b": [9]}
groups = defaultdict(list, d)

Question 7

How to get more info on a function?

Answer 7

help(torch.where) #python
torch.where? #Jupyter

Question 8

How to give a selection of arguments?

Answer 8

``` from typing import Literal

Reduction = Literal[“none”, “mean”, “sum”]

def my_loss(x, reduction: Reduction = “mean”):
…
~~~

Question 9

How to type optional arguments?

Answer 9

```
Optional[torch.Tensor]
x: torch.Tensor | None = None
~~~

Question 10

What are common types in PyTorch?

Answer 10

def forward_pass(model: nn.Module, x: torch.Tensor) -> torch.Tensor:
    return model(x)

Question 11

How to get infinity and -infinity?

Answer 11

neg_inf = float("-inf")