[hotfix][data]Fix some Python code defects in ray data scanned by PyLint tool

[daiping8]

Overview

We scanned the ray data code using the PyLint tool and found some defects. Here are some scan results based on ray 2.46 version:
"ray/python/ray/data/read_api.py:3214:4: R1705: Unnecessary "elif" after "return", remove the leading "el" from "elif" (no-else-return)
ray/python/ray/data/datasource/file_based_datasource.py:276:20: R1730: Consider using 'num_threads = min(num_threads, len(read_paths))' instead of unnecessary if block (consider-using-min-builtin)
R1705: Unnecessary "else" after "return", remove the "else" and de-indent the code inside it (no-else-return)"
Scanning the latest branch of the master will also yield similar results

Why are these changes needed?

The modifications in PR do not affect the code logic and functionality, nor do they affect existing unit test cases. The aim is to reduce code complexity and redundant code without changing the code logic, and enhance the readability of ray code.

Related issue number

Closes #53881

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[gemini-code-assist]

Summary of Changes

Hello @daiping8, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

I've implemented a series of targeted hotfixes to address Python code defects identified by the PyLint tool within the Ray data module. The primary goal of these changes is to enhance code readability and reduce complexity without altering any existing logic or functionality. This includes simplifying conditional statements, optimizing control flow by removing unnecessary else and elif blocks after return statements, and leveraging Python's built-in functions for more concise expressions. These improvements contribute to a cleaner and more maintainable codebase.

Highlights

• Code Simplification: I've refactored conditional checks to use a tuple with isinstance(), making the code more readable and compact.
• Control Flow Optimization: I've removed redundant else and elif blocks that followed return statements, which improves code flow and adheres to best practices for early exits.
• Pythonic Code Refinement: I've replaced an if block with the min() builtin function for calculating thread counts, leading to more concise and Pythonic code.

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[gemini-code-assist]

Code Review

This pull request addresses several PyLint code defects, improving code style and readability. The changes are correct and beneficial. I have one suggestion regarding the type of exception being raised for unsupported input types, which would improve the correctness of error handling.