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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 

28 

29from typing import ( 

30 TYPE_CHECKING, 

31 Any, 

32 Optional, 

33 Type, 

34) 

35 

36from .file import FileFormatter 

37 

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 

40 

41 

42class JsonFormatter(FileFormatter): 

43 """Interface for reading and writing Python objects to and from JSON files. 

44 """ 

45 extension = ".json" 

46 

47 unsupportedParameters = None 

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

49 

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

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

52 

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. 

59 

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 

71 

72 return data 

73 

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

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

76 

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

78 the approach of the simplejson module. 

79 

80 Parameters 

81 ---------- 

82 inMemoryDataset : `object` 

83 Object to serialize. 

84 

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)) 

94 

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

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

97 

98 Parameters 

99 ---------- 

100 serializedDataset : `bytes` 

101 Bytes object to unserialize. 

102 pytype : `class`, optional 

103 Not used by this implementation. 

104 

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 

115 

116 return data 

117 

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

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

120 

121 Parameters 

122 ---------- 

123 inMemoryDataset : `object` 

124 Object to serialize 

125 

126 Returns 

127 ------- 

128 serializedDataset : `bytes` 

129 bytes representing the serialized dataset. 

130 

131 Raises 

132 ------ 

133 Exception 

134 The object could not be serialized. 

135 """ 

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

137 

138 def _coerceType(self, inMemoryDataset: Any, storageClass: StorageClass, 

139 pytype: Optional[Type[Any]] = None) -> Any: 

140 """Coerce the supplied inMemoryDataset to type `pytype`. 

141 

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. 

150 

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