Coverage for python/lsst/daf/butler/formatters/json.py : 77%

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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 Either data as Python object read from JSON file, or None
64 if the file could not be opened.
65 """
66 try:
67 with open(path, "rb") as fd:
68 data = self._fromBytes(fd.read(), pytype)
69 except FileNotFoundError:
70 data = None
72 return data
74 def _writeFile(self, inMemoryDataset: Any) -> None:
75 """Write the in memory dataset to file on disk.
77 Will look for `_asdict()` method to aid JSON serialization, following
78 the approach of the simplejson module.
80 Parameters
81 ----------
82 inMemoryDataset : `object`
83 Object to serialize.
85 Raises
86 ------
87 Exception
88 The file could not be written.
89 """
90 with open(self.fileDescriptor.location.path, "wb") as fd:
91 if hasattr(inMemoryDataset, "_asdict"):
92 inMemoryDataset = inMemoryDataset._asdict()
93 fd.write(self._toBytes(inMemoryDataset))
95 def _fromBytes(self, serializedDataset: bytes, pytype: Optional[Type[Any]] = None) -> Any:
96 """Read the bytes object as a python object.
98 Parameters
99 ----------
100 serializedDataset : `bytes`
101 Bytes object to unserialize.
102 pytype : `class`, optional
103 Not used by this implementation.
105 Returns
106 -------
107 inMemoryDataset : `object`
108 The requested data as a Python object or None if the string could
109 not be read.
110 """
111 try:
112 data = json.loads(serializedDataset)
113 except json.JSONDecodeError:
114 data = None
116 return data
118 def _toBytes(self, inMemoryDataset: Any) -> bytes:
119 """Write the in memory dataset to a bytestring.
121 Parameters
122 ----------
123 inMemoryDataset : `object`
124 Object to serialize
126 Returns
127 -------
128 serializedDataset : `bytes`
129 bytes representing the serialized dataset.
131 Raises
132 ------
133 Exception
134 The object could not be serialized.
135 """
136 return json.dumps(inMemoryDataset, ensure_ascii=False).encode()
138 def _coerceType(self, inMemoryDataset: Any, storageClass: StorageClass,
139 pytype: Optional[Type[Any]] = None) -> Any:
140 """Coerce the supplied inMemoryDataset to type `pytype`.
142 Parameters
143 ----------
144 inMemoryDataset : `object`
145 Object to coerce to expected type.
146 storageClass : `StorageClass`
147 StorageClass associated with `inMemoryDataset`.
148 pytype : `type`, optional
149 Override type to use for conversion.
151 Returns
152 -------
153 inMemoryDataset : `object`
154 Object of expected type `pytype`.
155 """
156 if pytype is not None and not hasattr(builtins, pytype.__name__):
157 if storageClass.isComposite(): 157 ↛ 159line 157 didn't jump to line 159, because the condition on line 157 was never false
158 inMemoryDataset = storageClass.delegate().assemble(inMemoryDataset, pytype=pytype)
159 elif not isinstance(inMemoryDataset, pytype):
160 # Hope that we can pass the arguments in directly
161 inMemoryDataset = pytype(inMemoryDataset)
162 return inMemoryDataset