Coverage for python/lsst/daf/butler/formatters/json.py : 80%

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1# This file is part of daf_butler.
2#
3# Developed for the LSST Data Management System.
4# This product includes software developed by the LSST Project
5# (http://www.lsst.org).
6# See the COPYRIGHT file at the top-level directory of this distribution
7# for details of code ownership.
8#
9# This program is free software: you can redistribute it and/or modify
10# it under the terms of the GNU General Public License as published by
11# the Free Software Foundation, either version 3 of the License, or
12# (at your option) any later version.
13#
14# This program is distributed in the hope that it will be useful,
15# but WITHOUT ANY WARRANTY; without even the implied warranty of
16# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17# GNU General Public License for more details.
18#
19# You should have received a copy of the GNU General Public License
20# along with this program. If not, see <http://www.gnu.org/licenses/>.
22from __future__ import annotations
24__all__ = ("JsonFormatter", )
26import builtins
27import json
29from typing import (
30 TYPE_CHECKING,
31 Any,
32 Optional,
33 Type,
34)
36from .file import FileFormatter
38if TYPE_CHECKING: 38 ↛ 39line 38 didn't jump to line 39, because the condition on line 38 was never true
39 from lsst.daf.butler import StorageClass
42class JsonFormatter(FileFormatter):
43 """Interface for reading and writing Python objects to and from JSON files.
44 """
45 extension = ".json"
47 unsupportedParameters = None
48 """This formatter does not support any parameters (`frozenset`)"""
50 def _readFile(self, path: str, pytype: Optional[Type[Any]] = None) -> Any:
51 """Read a file from the path in JSON format.
53 Parameters
54 ----------
55 path : `str`
56 Path to use to open JSON format file.
57 pytype : `class`, optional
58 Not used by this implementation.
60 Returns
61 -------
62 data : `object`
63 Data as Python object read from JSON file.
64 """
65 with open(path, "rb") as fd:
66 data = self._fromBytes(fd.read(), pytype)
68 return data
70 def _writeFile(self, inMemoryDataset: Any) -> None:
71 """Write the in memory dataset to file on disk.
73 Will look for `_asdict()` method to aid JSON serialization, following
74 the approach of the simplejson module.
76 Parameters
77 ----------
78 inMemoryDataset : `object`
79 Object to serialize.
81 Raises
82 ------
83 Exception
84 The file could not be written.
85 """
86 with open(self.fileDescriptor.location.path, "wb") as fd:
87 fd.write(self._toBytes(inMemoryDataset))
89 def _fromBytes(self, serializedDataset: bytes, pytype: Optional[Type[Any]] = None) -> Any:
90 """Read the bytes object as a python object.
92 Parameters
93 ----------
94 serializedDataset : `bytes`
95 Bytes object to unserialize.
96 pytype : `class`, optional
97 Not used by this implementation.
99 Returns
100 -------
101 inMemoryDataset : `object`
102 The requested data as a Python object or None if the string could
103 not be read.
104 """
105 try:
106 data = json.loads(serializedDataset)
107 except json.JSONDecodeError:
108 data = None
110 return data
112 def _toBytes(self, inMemoryDataset: Any) -> bytes:
113 """Write the in memory dataset to a bytestring.
115 Parameters
116 ----------
117 inMemoryDataset : `object`
118 Object to serialize
120 Returns
121 -------
122 serializedDataset : `bytes`
123 bytes representing the serialized dataset.
125 Raises
126 ------
127 Exception
128 The object could not be serialized.
129 """
130 if hasattr(inMemoryDataset, "_asdict"):
131 inMemoryDataset = inMemoryDataset._asdict()
132 return json.dumps(inMemoryDataset, ensure_ascii=False).encode()
134 def _coerceType(self, inMemoryDataset: Any, storageClass: StorageClass,
135 pytype: Optional[Type[Any]] = None) -> Any:
136 """Coerce the supplied inMemoryDataset to type `pytype`.
138 Parameters
139 ----------
140 inMemoryDataset : `object`
141 Object to coerce to expected type.
142 storageClass : `StorageClass`
143 StorageClass associated with `inMemoryDataset`.
144 pytype : `type`, optional
145 Override type to use for conversion.
147 Returns
148 -------
149 inMemoryDataset : `object`
150 Object of expected type `pytype`.
151 """
152 if inMemoryDataset is not None and pytype is not None and not hasattr(builtins, pytype.__name__):
153 if storageClass.isComposite(): 153 ↛ 155line 153 didn't jump to line 155, because the condition on line 153 was never false
154 inMemoryDataset = storageClass.delegate().assemble(inMemoryDataset, pytype=pytype)
155 elif not isinstance(inMemoryDataset, pytype):
156 # Hope that we can pass the arguments in directly
157 inMemoryDataset = pytype(inMemoryDataset)
158 return inMemoryDataset