Coverage for python/lsst/daf/butler/formatters/json.py: 81%

43 statements  

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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/>. 

21 

22from __future__ import annotations 

23 

24__all__ = ("JsonFormatter",) 

25 

26import builtins 

27import json 

28from typing import TYPE_CHECKING, Any, Optional, Type 

29 

30from .file import FileFormatter 

31 

32if TYPE_CHECKING: 32 ↛ 33line 32 didn't jump to line 33, because the condition on line 32 was never true

33 from lsst.daf.butler import StorageClass 

34 

35 

36class JsonFormatter(FileFormatter): 

37 """Formatter implementation for JSON files.""" 

38 

39 extension = ".json" 

40 

41 unsupportedParameters = None 

42 """This formatter does not support any parameters (`frozenset`)""" 

43 

44 def _readFile(self, path: str, pytype: Optional[Type[Any]] = None) -> Any: 

45 """Read a file from the path in JSON format. 

46 

47 Parameters 

48 ---------- 

49 path : `str` 

50 Path to use to open JSON format file. 

51 pytype : `class`, optional 

52 Not used by this implementation. 

53 

54 Returns 

55 ------- 

56 data : `object` 

57 Data as Python object read from JSON file. 

58 """ 

59 with open(path, "rb") as fd: 

60 data = self._fromBytes(fd.read(), pytype) 

61 

62 return data 

63 

64 def _writeFile(self, inMemoryDataset: Any) -> None: 

65 """Write the in memory dataset to file on disk. 

66 

67 Will look for `_asdict()` method to aid JSON serialization, following 

68 the approach of the simplejson module. 

69 

70 Parameters 

71 ---------- 

72 inMemoryDataset : `object` 

73 Object to serialize. 

74 

75 Raises 

76 ------ 

77 Exception 

78 The file could not be written. 

79 """ 

80 self.fileDescriptor.location.uri.write(self._toBytes(inMemoryDataset)) 

81 

82 def _fromBytes(self, serializedDataset: bytes, pytype: Optional[Type[Any]] = None) -> Any: 

83 """Read the bytes object as a python object. 

84 

85 Parameters 

86 ---------- 

87 serializedDataset : `bytes` 

88 Bytes object to unserialize. 

89 pytype : `class`, optional 

90 Not used by this implementation. 

91 

92 Returns 

93 ------- 

94 inMemoryDataset : `object` 

95 The requested data as a Python object or None if the string could 

96 not be read. 

97 """ 

98 try: 

99 data = json.loads(serializedDataset) 

100 except json.JSONDecodeError: 

101 data = None 

102 

103 return data 

104 

105 def _toBytes(self, inMemoryDataset: Any) -> bytes: 

106 """Write the in memory dataset to a bytestring. 

107 

108 Parameters 

109 ---------- 

110 inMemoryDataset : `object` 

111 Object to serialize 

112 

113 Returns 

114 ------- 

115 serializedDataset : `bytes` 

116 bytes representing the serialized dataset. 

117 

118 Raises 

119 ------ 

120 Exception 

121 The object could not be serialized. 

122 """ 

123 # For example, Pydantic models have a .json method so use it. 

124 try: 

125 return inMemoryDataset.json().encode() 

126 except AttributeError: 

127 pass 

128 

129 if hasattr(inMemoryDataset, "_asdict"): 

130 inMemoryDataset = inMemoryDataset._asdict() 

131 return json.dumps(inMemoryDataset, ensure_ascii=False).encode() 

132 

133 def _coerceType( 

134 self, inMemoryDataset: Any, writeStorageClass: StorageClass, readStorageClass: StorageClass 

135 ) -> Any: 

136 """Coerce the supplied inMemoryDataset to the correct python type. 

137 

138 Parameters 

139 ---------- 

140 inMemoryDataset : `object` 

141 Object to coerce to expected type. 

142 writeStorageClass : `StorageClass` 

143 Storage class used to serialize this data. 

144 readStorageClass : `StorageClass` 

145 Storage class requested as the outcome. 

146 

147 Returns 

148 ------- 

149 inMemoryDataset : `object` 

150 Object of expected type ``readStorageClass.pytype``. 

151 """ 

152 if inMemoryDataset is not None and not hasattr(builtins, readStorageClass.pytype.__name__): 

153 if readStorageClass.isComposite(): 

154 inMemoryDataset = readStorageClass.delegate().assemble( 

155 inMemoryDataset, pytype=readStorageClass.pytype 

156 ) 

157 elif not isinstance(inMemoryDataset, readStorageClass.pytype): 

158 # JSON data are returned as simple python types. 

159 # The content will match the written storage class. 

160 # Pydantic models have their own scheme. 

161 try: 

162 inMemoryDataset = writeStorageClass.pytype.parse_obj(inMemoryDataset) 

163 except AttributeError: 

164 # Hope that we can pass the arguments in directly 

165 inMemoryDataset = writeStorageClass.pytype(inMemoryDataset) 

166 inMemoryDataset = readStorageClass.coerce_type(inMemoryDataset) 

167 return inMemoryDataset