Fix ICM 51000001082652: VMBackup extension fails to import on Python 3.13+

[vupadhyay-ms]

The Issue

• ICM: 51000001082652

Customer VM (Ubuntu 26.04 / Py 3.14) fails backup. Extension log shows:

File ".../WaagentLib.py", line 26, in <module>
    import crypt
ModuleNotFoundError: No module named 'crypt'

File ".../WAAgentUtil.py", line 69, in <module>
    import imp
ModuleNotFoundError: No module named 'imp'

File "main/handle.py", line 40, in <module>
    from mounts import Mounts

---

The 3 stdlibs

Module	Deprecated	REMOVED in	Used in	Fails on
crypt	Py 3.11	Py 3.13	WaagentLib.py:26 (bare import crypt)	Ubuntu 26.04 / Py 3.14
distutils	Py 3.10	Py 3.12	WaagentLib.py:59 (from distutils.version import LooseVersion)	Debian 13, RHEL 10, Fedora 39+
imp	Py 3.4	Py 3.12	WAAgentUtil.py:69 (import imp fallback)	Same as above

Python removed these modules. Our code imports them unconditionally → extension crashes at file-load time → VMExtensionProvisioningTimeout → customer backup fails.

---

History (why previous fix was reverted)

1. Nov 2025 — PR #2124 tried the same fix. Merged.
2. Apr 2026 — Broke Py 2.7 VMs → ICM 783505554 (Sev2). Root cause: 2 subtle bugs:
   • Unicode → in fallback class docstring → Py 2 SyntaxError at parse time
   • except ImportError failed to catch AttributeError from importlib.util.module_from_spec on Py 2.7
3. Apr 2026 — PR #2163 fully reverted Updates for deprecated modules in Python 3.12 and Invalid escape sequence issues #2124.
4. Result — original Py 3.13+ crash returned → this ICM.

This PR re-lands the fix with those 2 bugs corrected.

---

The Fix — 5 edits, 2 files

VMBackup/main/WaagentLib.py

Edit 1 — Add PEP 263 encoding declaration

# -*- coding: utf-8 -*-

Prevents future Unicode-in-source regressions (prevents ICM 783505554 class of bug).

Edit 2 — Wrap import crypt

try:
    import crypt
except ImportError:
    crypt = None

crypt is dead code (VMBackup never calls gen_password_hash). Wrapping stops the crash.

Edit 3 — Replace distutils.LooseVersion with 3-tier ladder

try:
    from packaging.version import Version as LooseVersion       # Tier 1: modern
except ImportError:
    try:
        from distutils.version import LooseVersion              # Tier 2: legacy stdlib
    except ImportError:
        class LooseVersion(object): ...                          # Tier 3: ASCII-only fallback

Guarantees LooseVersion resolves on every Python 2.7 → 3.14. Tier 3 class is identical to PR #2124's, with 2 corrections: (a) inherits from object for Py 2.7 rich-comparison correctness, (b) ASCII -> instead of Unicode →.

Edit 4 — Defensive guard in gen_password_hash()

if crypt is None:
    raise NotImplementedError("gen_password_hash requires the 'crypt' stdlib module...")

Never hit today; fails loudly if some future caller reaches this on Py 3.13+.

VMBackup/main/Utils/WAAgentUtil.py

Edit 5 — Replace exception-based fallback with capability check

if importlib_util is not None and hasattr(importlib_util, 'module_from_spec'):
    # Modern path — Py 3.5+
    spec = importlib_util.spec_from_file_location('waagent', agentPath)
    waagent = importlib_util.module_from_spec(spec)
    spec.loader.exec_module(waagent)
else:
    # Legacy path — Py 2.6–3.4 only
    import imp
    waagent = imp.load_source('waagent', agentPath)

Testing —

Test Setup: Azure Ubuntu 24.04 VM + python3.10 / 3.12 / 3.13 / 3.14 (via deadsnakes PPA) + Docker python:2.7 for regression coverage.

Test	Py 2.7	Py 3.10	Py 3.12	Py 3.13	Py 3.14
py_compile on both files	✅	✅	✅	✅	✅
Full import chain	✅	✅	✅	✅	✅
handle.py -enable exit 0	—	✅	✅	✅	✅

[vupadhyay-ms]

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