Remove six and Python 2 compatibility code

[s-t-e-v-e-n-k]

Now that Python 3.4 is the lowest supported version, we can remove a large amount of code that support versions before it, as well as use of six, as well as the entire _compat module. Drive-by removing the pkg_resources check from setup.py since setuptools 39 is now ten years old.

Summary by CodeRabbit

Release Notes

• Chores
  • Removed Python 2 and early Python 3 compatibility code and dependencies throughout the project.
  • Simplified internal logic and module initialization by eliminating version-specific workarounds and conditionals.
  • Modernized setup configuration and dependency requirements to focus exclusively on Python 3+ standards.
  • Overall codebase cleanup improves maintainability and reduces complexity.

[coderabbitai]

Walkthrough

This PR removes Python 2 support from wirerope by eliminating the six and inspect2 dependencies, stripping version-conditional code from callable detection and runtime dispatch, and simplifying build configuration. Runtime logic and type classification are unified to assume Python 3.

Changes

Python 2 compatibility removal

Layer / File(s)	Summary
Build configuration and dependency cleanup setup.cfg, setup.py	install_requires dependencies on six, inspect2, and singledispatch are removed. The setuptools version assertion in setup.py is dropped.
Callable classification method simplification wirerope/callable.py	Imports switch to standard-library inspect. is_boundmethod, is_barefunction, is_member, and is_classmethod predicates are rewritten to single unified implementations, removing six.PY2/six.PY3/six.PY34 branches and version-specific heuristics.
Runtime dispatch and initialization updates wirerope/rope.py, wirerope/wire.py	Imports switch to standard-library functools. WireRope.__call__ dispatch simplifies to a single __qualname__ check. Wire.__init__ drops Py2-specific functools.partial attribute handling.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Poem

🐰 Python 2 has bid farewell,
No more six or shims to dwell,
Callable methods bloom so bright,
Dispatch logic cleaned up right,
Wirerope hops to Python 3's light! 🌟

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 37.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Remove six and Python 2 compatibility code' directly and clearly matches the main objective of the PR: eliminating Python 2 compatibility code and removing the six library dependency.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@wirerope/callable.py`:
- Line 1: Remove the obsolete Python 2 compatibility import by deleting the line
"from __future__ import absolute_import" at the top of callable.py; no other
code changes required since the project no longer targets Python 2 and this
import has no effect in Python 3.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 75a581b5-b45f-4474-b3e5-de9d061ccb4f

📥 Commits

Reviewing files that changed from the base of the PR and between e5e0576 and 601854d.

📒 Files selected for processing (6)

• setup.cfg
• setup.py
• wirerope/_compat.py
• wirerope/callable.py
• wirerope/rope.py
• wirerope/wire.py

💤 Files with no reviewable changes (3)

• setup.cfg
• wirerope/_compat.py
• setup.py

[coderabbitai]

🧹 Nitpick | 🔵 Trivial | 💤 Low value

Consider removing the obsolete __future__ import.

from __future__ import absolute_import has no effect in Python 3. Since this PR removes Python 2 support, this import can be removed for consistency.

🧹 Suggested cleanup

-from __future__ import absolute_import
-
 import inspect

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

	from __future__ import absolute_import
	import inspect

🧰 Tools

🪛 Ruff (0.15.15)

[warning] 1-1: Unnecessary __future__ import absolute_import for target Python version

Remove unnecessary __future__ import

(UP010)

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@wirerope/callable.py` at line 1, Remove the obsolete Python 2 compatibility
import by deleting the line "from __future__ import absolute_import" at the top
of callable.py; no other code changes required since the project no longer
targets Python 2 and this import has no effect in Python 3.