pillow 10.4.0: Querying Pillow format registries or codecs directly without Image.init returns empty tables or false negatives, and openable formats like PSD are absent from Image.SAVE

A naive model would check `'PNG' in Image.SAVE` or `features.check('png')` without calling `Image.init()`, or assume formats listed in `Image.registered_extensions()` / `Image.OPEN` (like PSD) can be saved.
The wrong approach fails silently with false negatives (e.g. `'PNG' in Image.SAVE` returns `False` because registries are empty before `Image.init()`) or fails loudly at runtime with `KeyError: 'PSD'` when saving read-only formats despite clean static type checks.

{"case":{"caseId":"case:sha256:58eec5cbe25097cf99b38de97b8a862a90e07b2fd4afd531f1223c2febe17cbe","constraints":{"runtime":"python"},"contract":["assert len(Image.SAVE) == 0 before Image.init()","assert 'PNG' not in Image.SAVE before Image.init()","assert 'PNG' in Image.SAVE after Image.init()","assert 'png' not in Image.SAVE and '.jpg' not in Image.SAVE","assert Image.EXTENSION['.jpg'] == 'JPEG'","assert 'PSD' in Image.OPEN and 'PSD' not in Image.SAVE","assert features.check('png') is False and features.check('zlib') is True"],"goal":"Querying Pillow format registries or codecs directly without Image.init returns empty tables or false negatives, and openable formats like PSD are absent from Image.SAVE","kind":"HOW","packages":["pkg:pypi/pillow@10.4.0"],"schemaVersion":1,"symbols":["PIL.Image.init","PIL.Image.SAVE","PIL.Image.OPEN","PIL.Image.EXTENSION","PIL.Image.registered_extensions","PIL.features.check"]},"contractCommand":["python","test/contract.py"],"environment":{"arch":"x64","ecosystem":"pypi","executionContext":"python","language":"python","os":"linux","packageManager":"pip","runtime":"python","schemaVersion":1},"license":"MIT-0","packages":["pkg:pypi/pillow@10.4.0"],"schemaVersion":1,"symbols":["PIL.Image.init","PIL.Image.SAVE","PIL.Image.OPEN","PIL.Image.EXTENSION","PIL.Image.registered_extensions","PIL.features.check"],"verifierAdapter":"python@1"}

pillow==10.4.0

from PIL import Image


def is_saveable_format(format_or_extension: str) -> bool:
    """Return True if Pillow can save to the specified format name or file extension."""
    Image.init()
    target = format_or_extension.strip()
    if target.startswith("."):
        canonical = Image.EXTENSION.get(target.lower())
        return bool(canonical and canonical in Image.SAVE)

    canonical_direct = target.upper()
    if canonical_direct in Image.SAVE:
        return True

    canonical_ext = Image.EXTENSION.get(f".{target.lower()}")
    return bool(canonical_ext and canonical_ext in Image.SAVE)

import io
import os
import sys
import warnings

# Add parent directory to path so src can be imported
sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))

from PIL import Image, features
from src.format_checker import is_saveable_format


def test_lazy_initialization_trap():
    # Before Image.init(), format registries are completely unpopulated.
    # A naive model expects 'PNG' in Image.SAVE immediately after import.
    assert len(Image.SAVE) == 0
    assert len(Image.OPEN) == 0
    assert len(Image.EXTENSION) == 0
    assert "PNG" not in Image.SAVE
    assert ".png" not in Image.EXTENSION


def test_save_registry_after_init():
    # Calling Image.init() populates the internal plugin registries.
    Image.init()
    assert len(Image.SAVE) > 0
    assert len(Image.OPEN) > 0
    assert len(Image.EXTENSION) > 0
    assert "PNG" in Image.SAVE
    assert "JPEG" in Image.SAVE


def test_case_and_extension_normalization():
    # Image.SAVE keys are strictly uppercase canonical format names,
    # NOT file extensions, NOT lowercase names, and NOT extension aliases (e.g. JPG).
    assert "png" not in Image.SAVE
    assert ".png" not in Image.SAVE
    assert "jpg" not in Image.SAVE
    assert "JPG" not in Image.SAVE
    assert ".jpg" not in Image.SAVE

    # File extensions must be mapped through Image.EXTENSION to find the canonical key
    assert Image.EXTENSION[".jpg"] == "JPEG"
    assert Image.EXTENSION[".jpeg"] == "JPEG"
    assert Image.EXTENSION[".png"] == "PNG"
    assert Image.EXTENSION[".jpg"] in Image.SAVE


def test_read_vs_save_asymmetry():
    # registered_extensions() / Image.OPEN only prove decoders (read capability),
    # NOT encoder/save capability.
    assert "PSD" in Image.OPEN
    assert ".psd" in Image.registered_extensions()
    assert "PSD" not in Image.SAVE

    # Attempting to save an open-only format fails with KeyError
    img = Image.new("RGB", (8, 8), color="white")
    sink = io.BytesIO()
    try:
        img.save(sink, format="PSD")
        raise AssertionError("Expected KeyError when saving unsupported PSD format")
    except KeyError as exc:
        assert exc.args[0] == "PSD"


def test_features_check_codec_naming():
    # features.check does not accept format strings like 'png' or 'jpeg'.
    # It requires low-level codec names like 'zlib' and 'jpg'.
    with warnings.catch_warnings(record=True) as recorded_warnings:
        warnings.simplefilter("always")
        assert features.check("png") is False
        assert features.check("jpeg") is False
        assert len(recorded_warnings) == 2
        assert any("Unknown feature 'png'" in str(w.message) for w in recorded_warnings)
        assert any("Unknown feature 'jpeg'" in str(w.message) for w in recorded_warnings)

    assert features.check("zlib") is True
    assert features.check("jpg") is True


def test_format_checker_helper():
    assert is_saveable_format(".png") is True
    assert is_saveable_format(".jpg") is True
    assert is_saveable_format(".jpeg") is True
    assert is_saveable_format("png") is True
    assert is_saveable_format("jpg") is True
    assert is_saveable_format("JPEG") is True
    assert is_saveable_format(".psd") is False
    assert is_saveable_format("psd") is False
    assert is_saveable_format("PSD") is False
    assert is_saveable_format(".nonexistent") is False


if __name__ == "__main__":
    test_lazy_initialization_trap()
    test_save_registry_after_init()
    test_case_and_extension_normalization()
    test_read_vs_save_asymmetry()
    test_features_check_codec_naming()
    test_format_checker_helper()
    print("All contract assertions passed successfully.")