Coverage for python/lsst/daf/butler/formatters/json.py: 75%

45 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 dataclasses 

28import json 

29from typing import TYPE_CHECKING, Any, Optional, Type 

30 

31from .file import FileFormatter 

32 

33if TYPE_CHECKING: 33 ↛ 34line 33 didn't jump to line 34, because the condition on line 33 was never true

34 from lsst.daf.butler import StorageClass 

35 

36 

37class JsonFormatter(FileFormatter): 

38 """Formatter implementation for JSON files.""" 

39 

40 extension = ".json" 

41 

42 unsupportedParameters = None 

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

44 

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

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

47 

48 Parameters 

49 ---------- 

50 path : `str` 

51 Path to use to open JSON format file. 

52 pytype : `class`, optional 

53 Not used by this implementation. 

54 

55 Returns 

56 ------- 

57 data : `object` 

58 Data as Python object read from JSON file. 

59 """ 

60 with open(path, "rb") as fd: 

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

62 

63 return data 

64 

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

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

67 

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

69 the approach of the simplejson module. 

70 

71 Parameters 

72 ---------- 

73 inMemoryDataset : `object` 

74 Object to serialize. 

75 

76 Raises 

77 ------ 

78 Exception 

79 The file could not be written. 

80 """ 

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

82 

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

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

85 

86 Parameters 

87 ---------- 

88 serializedDataset : `bytes` 

89 Bytes object to unserialize. 

90 pytype : `class`, optional 

91 Not used by this implementation. 

92 

93 Returns 

94 ------- 

95 inMemoryDataset : `object` 

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

97 not be read. 

98 """ 

99 try: 

100 data = json.loads(serializedDataset) 

101 except json.JSONDecodeError: 

102 data = None 

103 

104 return data 

105 

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

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

108 

109 Parameters 

110 ---------- 

111 inMemoryDataset : `object` 

112 Object to serialize 

113 

114 Returns 

115 ------- 

116 serializedDataset : `bytes` 

117 bytes representing the serialized dataset. 

118 

119 Raises 

120 ------ 

121 Exception 

122 The object could not be serialized. 

123 """ 

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

125 try: 

126 return inMemoryDataset.json().encode() 

127 except AttributeError: 

128 pass 

129 

130 if hasattr(inMemoryDataset, "_asdict"): 

131 inMemoryDataset = inMemoryDataset._asdict() 

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

133 

134 def _coerceType( 

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

136 ) -> Any: 

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

138 

139 Parameters 

140 ---------- 

141 inMemoryDataset : `object` 

142 Object to coerce to expected type. 

143 writeStorageClass : `StorageClass` 

144 Storage class used to serialize this data. 

145 readStorageClass : `StorageClass` 

146 Storage class requested as the outcome. 

147 

148 Returns 

149 ------- 

150 inMemoryDataset : `object` 

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

152 """ 

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

154 if writeStorageClass.isComposite(): 

155 # We know we must be able to assemble the written 

156 # storage class. Coerce later to the read type. 

157 inMemoryDataset = writeStorageClass.delegate().assemble( 

158 inMemoryDataset, pytype=writeStorageClass.pytype 

159 ) 

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

161 # JSON data are returned as simple python types. 

162 # The content will match the written storage class. 

163 # Pydantic models have their own scheme. 

164 try: 

165 inMemoryDataset = writeStorageClass.pytype.parse_obj(inMemoryDataset) 

166 except AttributeError: 

167 if dataclasses.is_dataclass(writeStorageClass.pytype): 

168 # dataclasses accept key/value parameters. 

169 inMemoryDataset = writeStorageClass.pytype(**inMemoryDataset) 

170 else: 

171 # Hope that we can pass the arguments in directly 

172 inMemoryDataset = writeStorageClass.pytype(inMemoryDataset) 

173 # Coerce to the read storage class if necessary. 

174 return readStorageClass.coerce_type(inMemoryDataset)