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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 

22__all__ = ("PexConfigFormatter", ) 

23 

24import os.path 

25 

26from lsst.utils import doImport 

27from lsst.daf.butler.formatters.fileFormatter import FileFormatter 

28 

29 

30class PexConfigFormatter(FileFormatter): 

31 """Interface for reading and writing pex.config.Config objects from disk. 

32 """ 

33 extension = ".py" 

34 

35 def _readFile(self, path, pytype): 

36 """Read a pex.config.Config instance from the given file. 

37 

38 Parameters 

39 ---------- 

40 path : `str` 

41 Path to use to open the file. 

42 pytype : `class` 

43 Class to use to read the config file. 

44 

45 Returns 

46 ------- 

47 data : `lsst.pex.config.Config` 

48 Instance of class `pytype` read from config file. None 

49 if the file could not be opened. 

50 """ 

51 if not os.path.exists(path): 

52 return None 

53 instance = pytype() 

54 # Configs can only be loaded if you use the correct derived type, 

55 # but we can't really store the correct derive type in the StorageClass 

56 # because that"d be a huge proliferation of StorageClasses. 

57 # Instead, we use a bit of a hack: try to load using the base-class 

58 # Config, inspect the exception message to obtain the class we should 

59 # have used, import that, and try it instead. 

60 # TODO: clean this up, somehow. 

61 try: 

62 instance.load(path) 

63 return instance 

64 except AssertionError as err: 

65 msg = str(err) 

66 if not msg.startswith("config is of type"): 

67 raise RuntimeError("Unexpected assertion; cannot infer Config class type.") from err 

68 actualPyTypeStr = msg.split()[-1] 

69 actualPyType = doImport(actualPyTypeStr) 

70 instance = actualPyType() 

71 instance.load(path) 

72 return instance 

73 

74 def _writeFile(self, inMemoryDataset): 

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

76 

77 Parameters 

78 ---------- 

79 inMemoryDataset : `object` 

80 Object to serialize. 

81 

82 Raises 

83 ------ 

84 Exception 

85 The file could not be written. 

86 """ 

87 inMemoryDataset.save(self.fileDescriptor.location.path)