Coverage for python/lsst/daf/butler/formatters/jsonFormatter.py : 79%

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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/>.
22__all__ = ("JsonFormatter", )
24import builtins
25import json
27from lsst.daf.butler.formatters.fileFormatter import FileFormatter
30class JsonFormatter(FileFormatter):
31 """Interface for reading and writing Python objects to and from JSON files.
32 """
33 extension = ".json"
35 unsupportedParameters = None
36 """This formatter does not support any parameters (`frozenset`)"""
38 def _readFile(self, path, pytype=None):
39 """Read a file from the path in JSON format.
41 Parameters
42 ----------
43 path : `str`
44 Path to use to open JSON format file.
46 Returns
47 -------
48 data : `object`
49 Either data as Python object read from JSON file, or None
50 if the file could not be opened.
51 """
52 try:
53 with open(path, "rb") as fd:
54 data = self._fromBytes(fd.read(), pytype)
55 except FileNotFoundError:
56 data = None
58 return data
60 def _writeFile(self, inMemoryDataset):
61 """Write the in memory dataset to file on disk.
63 Will look for `_asdict()` method to aid JSON serialization, following
64 the approach of the simplejson module.
66 Parameters
67 ----------
68 inMemoryDataset : `object`
69 Object to serialize.
71 Raises
72 ------
73 Exception
74 The file could not be written.
75 """
76 with open(self.fileDescriptor.location.path, "wb") as fd:
77 if hasattr(inMemoryDataset, "_asdict"):
78 inMemoryDataset = inMemoryDataset._asdict()
79 fd.write(self._toBytes(inMemoryDataset))
81 def _fromBytes(self, serializedDataset, pytype=None):
82 """Read the bytes object as a python object.
84 Parameters
85 ----------
86 serializedDataset : `bytes`
87 Bytes object to unserialize.
88 pytype : `class`, optional
89 Not used by this implementation.
91 Returns
92 -------
93 inMemoryDataset : `object`
94 The requested data as a Python object or None if the string could
95 not be read.
96 """
97 try:
98 data = json.loads(serializedDataset)
99 except json.JSONDecodeError:
100 data = None
102 return data
104 def _toBytes(self, inMemoryDataset):
105 """Write the in memory dataset to a bytestring.
107 Parameters
108 ----------
109 inMemoryDataset : `object`
110 Object to serialize
112 Returns
113 -------
114 serializedDataset : `bytes`
115 bytes representing the serialized dataset.
117 Raises
118 ------
119 Exception
120 The object could not be serialized.
121 """
122 return json.dumps(inMemoryDataset, ensure_ascii=False).encode()
124 def _coerceType(self, inMemoryDataset, storageClass, pytype=None):
125 """Coerce the supplied inMemoryDataset to type `pytype`.
127 Parameters
128 ----------
129 inMemoryDataset : `object`
130 Object to coerce to expected type.
131 storageClass : `StorageClass`
132 StorageClass associated with `inMemoryDataset`.
133 pytype : `type`, optional
134 Override type to use for conversion.
136 Returns
137 -------
138 inMemoryDataset : `object`
139 Object of expected type `pytype`.
140 """
141 if not hasattr(builtins, pytype.__name__):
142 if storageClass.isComposite(): 142 ↛ 144line 142 didn't jump to line 144, because the condition on line 142 was never false
143 inMemoryDataset = storageClass.assembler().assemble(inMemoryDataset, pytype=pytype)
144 elif not isinstance(inMemoryDataset, pytype):
145 # Hope that we can pass the arguments in directly
146 inMemoryDataset = pytype(inMemoryDataset)
147 return inMemoryDataset