lazysafe
safely adopt python 3.15 lazy imports.
why it exists
python 3.15 ships PEP 810 explicit lazy
imports. lazy import json defers loading until first use. reported wins: ~2.9x
faster startup for import-heavy applications.
the catch: laziness changes when import-time side effects run. some libraries depend on them. under lazy mode, programs break in confusing ways.
lazysafe answers that question empirically.
install
pip install lazysafe
quickstart
# see which imports are safe to make lazy
lazysafe analyze src/
# show all modules including safe ones
lazysafe analyze src/ --all
# measure startup time
lazysafe measure python -m myapp --budget 500
what it does
lazysafe scans your Python source files and classifies every import statement by its side-effect risk:
| finding | meaning | action |
|---|---|---|
| SAFE | no side effects detected | safe to make lazy |
| RISKY | might have side effects | investigate before lazy |
| UNSAFE | side effect detected | keep eager |
| UNKNOWN | can't determine statically | needs further investigation |
side-effect rules
| code | what it detects | confidence |
|---|---|---|
| SE01 | module-level function calls | 0.6 |
| SE02 | foreign attribute assignment (monkeypatching) | 0.9 |
| SE03 | sys.path / sys.modules / os.environ mutation | 0.95 |
| SE04 | atexit / signal / logging registration | 0.85-0.9 |
| SE05 | module-level file I/O | 0.8 |
| SE06 | framework registration decorators (2+) | 0.5 |
| SE07 | importlib.import_module with computed names | 0.9 |
| SE08 | try/except ImportError with fallback patches | 0.7 |
what it does not do
- runtime lazy-loading for older pythons (no backport of PEP 810)
- patching third-party packages' code
- general linting/formatting (use ruff)
requirements
- python >= 3.11 (host running lazysafe)
- target programs using lazy import semantics require python >= 3.15
- linux, macos, windows
links
license
MIT
1 maintainer
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