_yaml.py

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# This file is part of sphgeom.
#
# Developed for the LSST Data Management System.
# This product includes software developed by the LSST Project
# (http://www.lsst.org).
# See the COPYRIGHT file at the top-level directory of this distribution
# for details of code ownership.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
"""Add support for YAML serialization of regions."""
 
__all__ = ()
 
# YAML representers and constructors are only useful if yaml itself can
# be imported.  If yaml can not be imported then there is no reason to
# break the entire module import of sphgeom.
try:
    import yaml
except ImportError:
    yaml = None
 
from ._sphgeom import (
    Box,
    Circle,
    ConvexPolygon,
    Ellipse,
    HtmPixelization,
    Mq3cPixelization,
    Region,
    Q3cPixelization,
)
 
 
if yaml:
    try:
        # CLoader is not always available
        from yaml import CLoader
    except ImportError:
        CLoader = None
 
    YamlLoaders = (yaml.Loader, yaml.FullLoader, yaml.SafeLoader, yaml.UnsafeLoader)
    if CLoader is not None:
        YamlLoaders += (CLoader,)
 
 
# Regions
 
def region_representer(dumper, data):
    """Represent a sphgeom region object in a form suitable for YAML.
 
    Stores the region as a mapping with a single ``encoded`` key
    storing the hex encoded byte string.
    """
    encoded = data.encode()
    return dumper.represent_mapping(f"lsst.sphgeom.{type(data).__name__}",
                                    {"encoded": encoded.hex()})
 
 
def region_constructor(loader, node):
    """Construct a sphgeom region from YAML"""
    mapping = loader.construct_mapping(node)
    encoded = bytes.fromhex(mapping["encoded"])
    # The generic Region base class can instantiate a region of the
    # correct type.
    return Region.decode(encoded)
 
 
# Register all the region classes with the same constructor and representer
if yaml:
    for region_class in (ConvexPolygon, Ellipse, Circle, Box):
        yaml.add_representer(region_class, region_representer)
 
        for loader in YamlLoaders:
            yaml.add_constructor(f"lsst.sphgeom.{region_class.__name__}", region_constructor, Loader=loader)
 
 
# Pixelization schemes
 
def pixel_representer(dumper, data):
    """Represent a pixelization in YAML
 
    Stored as the pixelization level in a mapping with a single key
    ``level``.
    """
    return dumper.represent_mapping(f"lsst.sphgeom.{type(data).__name__}",
                                    {"level": data.getLevel()})
 
 
def pixel_constructor(loader, node):
    """Construct a pixelization object from YAML.
    """
    mapping = loader.construct_mapping(node)
 
    className = node.tag
    pixelMap = {"lsst.sphgeom.Q3cPixelization": Q3cPixelization,
                "lsst.sphgeom.Mq3cPixelization": Mq3cPixelization,
                "lsst.sphgeom.HtmPixelization": HtmPixelization,
                }
 
    if className not in pixelMap:
        raise RuntimeError(f"Encountered unexpected class {className} associated with"
                           " sphgeom pixelization YAML constructor")
 
    return pixelMap[className](mapping["level"])
 
 
# All the pixelization schemes use the same approach with getLevel
if yaml:
    for pixelSchemeCls in (HtmPixelization, Q3cPixelization, Mq3cPixelization):
        yaml.add_representer(pixelSchemeCls, pixel_representer)
        for loader in YamlLoaders:
            yaml.add_constructor(f"lsst.sphgeom.{pixelSchemeCls.__name__}", pixel_constructor, Loader=loader)