huggingface/datasets

Consider using "Sequence" instead of "List"

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#5,354 opened on Dec 12, 2022

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Description

Feature request

Hi, please consider using Sequence type annotation instead of List in function arguments such as in Dataset.from_parquet(). It leads to type checking errors, see below.

How to reproduce

list_of_filenames = ["foo.parquet", "bar.parquet"]
ds = Dataset.from_parquet(list_of_filenames)

Expected mypy output:

Success: no issues found

Actual mypy output:

test.py:19: error: Argument 1 to "from_parquet" of "Dataset" has incompatible type "List[str]"; expected "Union[Union[str, bytes, PathLike[Any]], List[Union[str, bytes, PathLike[Any]]]]"  [arg-type]
test.py:19: note: "List" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
test.py:19: note: Consider using "Sequence" instead, which is covariant

Env: mypy 0.991, Python 3.10.0, datasets 2.7.1

Contributor guide

Research direction
Change type hint from List to Sequence in Dataset.from parquet() argument to fix mypy invariance error.
Tech stack
python
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
1
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Under 1 hour
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Active
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Clear
Prerequisites
Python
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
90