feat: lazy imports gapic v1

[hebaalazzeh]

Description

This PR initiates the rollout of our PEP 0810 lazy-loading architecture to google-api-core, starting with the gapic_v1 module.

By applying Python 3.15's native explicit lazy imports, we defer the eager execution of inner modules (like method.py and config.py) which recursively pull in massive third-party C-extensions like grpcio. This acts as the first step in addressing the high initialization latency and peak memory footprints we're seeing on Serverless cold-starts.

Older Python runtimes (3.14 and below) safely ignore the __lazy_modules__ set and fall back to standard eager execution, meaning this introduces zero backwards compatibility risk.

(Note: We use fully-qualified, hardcoded module strings rather than dynamic __name__ injection, and provide explicit type annotations (Set[str]), to ensure static analysis tools and type checkers can safely infer the proxies without complaints).

Related Documents

• Design Doc: go/sdk:api-core-lazy-loading
• Original GAPIC Generator Implementation PR: feat: implement native PEP 0810 lazy loading #17591

[gemini-code-assist]

Code Review

This pull request adds an import_profile test target to the CI script and attempts to implement lazy loading for gapic_v1 submodules using Python 3.15's __lazy_modules__ feature. However, a critical issue was identified: placing the imports inside a conditional block (sys.version_info < (3, 15)) prevents them from being executed at all on Python 3.15+, which will lead to AttributeErrors at runtime. To fix this, the imports should remain at the top level so that Python 3.15+ can lazily load them while older versions load them eagerly.

[parthea]

Similar to the feedback from #17679, please can you also add tests?

[parthea]

I'm going to switch this to draft until tests are added. Please mark this as ready for review once #17673 (review) is addressed

[hebaalazzeh]

/gemini review

[gemini-code-assist]

Code Review

This pull request implements PEP 0810 explicit lazy imports for Python 3.15+ in the gapic_v1 package and adds unit tests to verify both lazy and fallback eager import behaviors. Feedback points out a critical inconsistency when grpc is not installed: on Python 3.15+, the deferred imports prevent ImportError from being caught eagerly, resulting in missing dependencies being added to __all__ and causing runtime failures during wildcard imports. The reviewer suggests using importlib.util.find_spec to conditionally define lazy modules and imports based on the presence of grpc.

[hebaalazzeh]

/gemini review

[gemini-code-assist]

Code Review

This pull request attempts to implement lazy imports in gapic_v1 using a hypothetical Python 3.15 feature (__lazy_modules__ / PEP 810), falling back to eager imports on older versions. However, because this feature and PEP do not exist, the implementation currently results in eager imports on all Python versions. The reviewer recommends implementing standard lazy loading using PEP 562 (__getattr__ and __dir__), which is compatible with all supported Python versions (3.7+). This approach would also allow the accompanying unit tests to run and verify lazy loading behavior across all environments instead of being skipped on versions below 3.15.