Coverage for python/lsst/pipe/base/struct.py : 29%

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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#
23__all__ = ["Struct"]
26class Struct:
27 """A container to which you can add fields as attributes.
29 Parameters
30 ----------
31 keyArgs
32 keyword arguments specifying fields and their values.
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.
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.
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.
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).
52 Examples
53 --------
54 >>> myStruct = Struct(
55 >>> strVal = 'the value of the field named "strVal"',
56 >>> intVal = 35,
57 >>> )
59 """
61 def __init__(self, **keyArgs):
62 for name, val in keyArgs.items():
63 self.__safeAdd(name, val)
65 def __safeAdd(self, name, val):
66 """Add a field if it does not already exist and name does not start with ``__`` (two underscores).
68 Parameters
69 ----------
70 name : `str`
71 Name of field to add.
72 val : object
73 Value of field to add.
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)
86 def getDict(self):
87 """Get a dictionary of fields in this struct.
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()
96 def mergeItems(self, struct, *nameList):
97 """Copy specified fields from another struct, provided they don't already exist.
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.
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).
112 Examples
113 --------
114 For example::
116 foo.copyItems(other, "itemName1", "itemName2")
118 copies ``other.itemName1`` and ``other.itemName2`` into self.
119 """
120 for name in nameList:
121 self.__safeAdd(name, getattr(struct, name))
123 def copy(self):
124 """Make a one-level-deep copy (values are not copied).
126 Returns
127 -------
128 copy : `Struct`
129 One-level-deep copy of this Struct.
130 """
131 return Struct(**self.getDict())
133 def __eq__(self, other):
134 return self.__dict__ == other.__dict__
136 def __len__(self):
137 return len(self.__dict__)
139 def __repr__(self):
140 itemsStr = "; ".join(f"{name}={val}" for name, val in self.getDict().items())
141 return f"{self.__class__.__name__}({itemsStr})"