Is there a way to do Type Hinting for List Indices in Python?

Question

I’m really enjoying python types, but can’t seem to figure out how you might type a list with known length and indices.

Let’s say for working with bounding boxes (which contain a lot of information) we want to just store data in a list to reduce the size of the data structure… (as compared to storing in a dict)

For examples sake the structure would want to be -> List[List[x: int, y: int, w: int, h: int, frame: int]]

Is there a way to support type hinting in Python that would support hints for the indices?

Thanks!

Asked By: njho

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Source

Answer 1

As per the suggestions above @Barmar mentions lists shouldn’t be used for uniform collections.

Better to use a tuple, or better yet a dataclass or NamedTuple as per @Kraigolas and @Ry-

Answered By: njho

Answer 2

Lists are generally meant to be variable-size and homogeneous. What you’re describing (fixed length, heterogeneous) is more like a tuple, or, since the fields are labelled, a NamedTuple or dataclass, but, where your data is 2D, a Pandas DataFrame might make more sense. For example:

import pandas as pd

df = pd.DataFrame(
    [range(1, 6)],  # Dummy data just for example
    columns=['x', 'y', 'w', 'h', 'frame'])

>>> df
   x  y  w  h  frame
0  1  2  3  4      5
>>> df.dtypes
x        int64
y        int64
w        int64
h        int64
frame    int64
dtype: object

Of course, it depends why you’re using type hinting whether this will be better. If you just want to have well-defined types for your data, this is perfect. But for static typing, this might actually be more difficult [though I haven’t tried it myself, so correct me if I’m wrong].

Under the hood, Pandas uses NumPy arrays, which can be very compact.

Answered By: wjandrea

Is there a way to do Type Hinting for List Indices in Python?

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