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1# 

2# LSST Data Management System 

3# Copyright 2008, 2009, 2010, 2011 LSST Corporation. 

4# 

5# This product includes software developed by the 

6# LSST Project (http://www.lsst.org/). 

7# 

8# This program is free software: you can redistribute it and/or modify 

9# it under the terms of the GNU General Public License as published by 

10# the Free Software Foundation, either version 3 of the License, or 

11# (at your option) any later version. 

12# 

13# This program is distributed in the hope that it will be useful, 

14# but WITHOUT ANY WARRANTY; without even the implied warranty of 

15# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 

16# GNU General Public License for more details. 

17# 

18# You should have received a copy of the LSST License Statement and 

19# the GNU General Public License along with this program. If not, 

20# see <http://www.lsstcorp.org/LegalNotices/>. 

21# 

22 

23__all__ = ["Struct"] 

24 

25 

26class Struct: 

27 """A container to which you can add fields as attributes. 

28 

29 Parameters 

30 ---------- 

31 keyArgs 

32 keyword arguments specifying fields and their values. 

33 

34 Notes 

35 ----- 

36 Intended to be used for the return value from `~lsst.pipe.base.Task.run` and other `~lsst.pipe.base.Task` 

37 methods, and useful for any method that returns multiple values. 

38 

39 The intent is to allow accessing returned items by name, instead of unpacking a tuple. 

40 This makes the code much more robust and easier to read. It allows one to change what values are returned 

41 without inducing mysterious failures: adding items is completely safe, and removing or renaming items 

42 causes errors that are caught quickly and reported in a way that is easy to understand. 

43 

44 The primary reason for using Struct instead of dict is that the fields may be accessed as attributes, 

45 e.g. ``aStruct.foo`` instead of ``aDict["foo"]``. Admittedly this only saves a few characters, but it 

46 makes the code significantly more readable. 

47 

48 Struct is preferred over named tuples, because named tuples can be used as ordinary tuples, thus losing 

49 all the safety advantages of Struct. In addition, named tuples are clumsy to define and Structs 

50 are much more mutable (e.g. one can trivially combine Structs and add additional fields). 

51 

52 Examples 

53 -------- 

54 >>> myStruct = Struct( 

55 >>> strVal = 'the value of the field named "strVal"', 

56 >>> intVal = 35, 

57 >>> ) 

58 

59 """ 

60 

61 def __init__(self, **keyArgs): 

62 for name, val in keyArgs.items(): 

63 self.__safeAdd(name, val) 

64 

65 def __safeAdd(self, name, val): 

66 """Add a field if it does not already exist and name does not start with ``__`` (two underscores). 

67 

68 Parameters 

69 ---------- 

70 name : `str` 

71 Name of field to add. 

72 val : object 

73 Value of field to add. 

74 

75 Raises 

76 ------ 

77 RuntimeError 

78 Raised if name already exists or starts with ``__`` (two underscores). 

79 """ 

80 if hasattr(self, name): 

81 raise RuntimeError(f"Item {name!r} already exists") 

82 if name.startswith("__"): 

83 raise RuntimeError(f"Item name {name!r} invalid; must not begin with __") 

84 setattr(self, name, val) 

85 

86 def getDict(self): 

87 """Get a dictionary of fields in this struct. 

88 

89 Returns 

90 ------- 

91 structDict : `dict` 

92 Dictionary with field names as keys and field values as values. The values are shallow copies. 

93 """ 

94 return self.__dict__.copy() 

95 

96 def mergeItems(self, struct, *nameList): 

97 """Copy specified fields from another struct, provided they don't already exist. 

98 

99 Parameters 

100 ---------- 

101 struct : `Struct` 

102 `Struct` from which to copy. 

103 *nameList : `str` 

104 All remaining arguments are names of items to copy. 

105 

106 Raises 

107 ------ 

108 RuntimeError 

109 Raised if any item in nameList already exists in self (but any items before the conflicting item 

110 in nameList will have been copied). 

111 

112 Examples 

113 -------- 

114 For example:: 

115 

116 foo.copyItems(other, "itemName1", "itemName2") 

117 

118 copies ``other.itemName1`` and ``other.itemName2`` into self. 

119 """ 

120 for name in nameList: 

121 self.__safeAdd(name, getattr(struct, name)) 

122 

123 def copy(self): 

124 """Make a one-level-deep copy (values are not copied). 

125 

126 Returns 

127 ------- 

128 copy : `Struct` 

129 One-level-deep copy of this Struct. 

130 """ 

131 return Struct(**self.getDict()) 

132 

133 def __eq__(self, other): 

134 return self.__dict__ == other.__dict__ 

135 

136 def __len__(self): 

137 return len(self.__dict__) 

138 

139 def __repr__(self): 

140 itemsStr = "; ".join(f"{name}={val}" for name, val in self.getDict().items()) 

141 return f"{self.__class__.__name__}({itemsStr})"