Coverage for python/lsst/pipe/base/struct.py: 36%
27 statements
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« prev ^ index » next coverage.py v6.4.4, created at 2022-08-19 12:18 -0700
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#
23from __future__ import annotations
25__all__ = ["Struct"]
27from typing import Any, Dict
30class Struct:
31 """A container to which you can add fields as attributes.
33 Parameters
34 ----------
35 keyArgs
36 keyword arguments specifying fields and their values.
38 Notes
39 -----
40 Intended to be used for the return value from `~lsst.pipe.base.Task.run`
41 and other `~lsst.pipe.base.Task` methods, and useful for any method that
42 returns multiple values.
44 The intent is to allow accessing returned items by name, instead of
45 unpacking a tuple. This makes the code much more robust and easier to
46 read. It allows one to change what values are returned without inducing
47 mysterious failures: adding items is completely safe, and removing or
48 renaming items causes errors that are caught quickly and reported in a way
49 that is easy to understand.
51 The primary reason for using Struct instead of dict is that the fields may
52 be accessed as attributes, e.g. ``aStruct.foo`` instead of
53 ``aDict["foo"]``. Admittedly this only saves a few characters, but it
54 makes the code significantly more readable.
56 Struct is preferred over named tuples, because named tuples can be used as
57 ordinary tuples, thus losing all the safety advantages of Struct. In
58 addition, named tuples are clumsy to define and Structs are much more
59 mutable (e.g. one can trivially combine Structs and add additional fields).
61 Examples
62 --------
63 >>> myStruct = Struct(
64 >>> strVal = 'the value of the field named "strVal"',
65 >>> intVal = 35,
66 >>> )
68 """
70 def __init__(self, **keyArgs: Any):
71 for name, val in keyArgs.items():
72 self.__safeAdd(name, val)
74 def __safeAdd(self, name: str, val: Any) -> None:
75 """Add a field if it does not already exist and name does not start
76 with ``__`` (two underscores).
78 Parameters
79 ----------
80 name : `str`
81 Name of field to add.
82 val : object
83 Value of field to add.
85 Raises
86 ------
87 RuntimeError
88 Raised if name already exists or starts with ``__`` (two
89 underscores).
90 """
91 if hasattr(self, name):
92 raise RuntimeError(f"Item {name!r} already exists")
93 if name.startswith("__"):
94 raise RuntimeError(f"Item name {name!r} invalid; must not begin with __")
95 setattr(self, name, val)
97 def getDict(self) -> Dict[str, Any]:
98 """Get a dictionary of fields in this struct.
100 Returns
101 -------
102 structDict : `dict`
103 Dictionary with field names as keys and field values as values.
104 The values are shallow copies.
105 """
106 return self.__dict__.copy()
108 def mergeItems(self, struct: Struct, *nameList: str) -> None:
109 """Copy specified fields from another struct, provided they don't
110 already exist.
112 Parameters
113 ----------
114 struct : `Struct`
115 `Struct` from which to copy.
116 *nameList : `str`
117 All remaining arguments are names of items to copy.
119 Raises
120 ------
121 RuntimeError
122 Raised if any item in nameList already exists in self (but any
123 items before the conflicting item in nameList will have been
124 copied).
126 Examples
127 --------
128 For example::
130 foo.copyItems(other, "itemName1", "itemName2")
132 copies ``other.itemName1`` and ``other.itemName2`` into self.
133 """
134 for name in nameList:
135 self.__safeAdd(name, getattr(struct, name))
137 def copy(self) -> Struct:
138 """Make a one-level-deep copy (values are not copied).
140 Returns
141 -------
142 copy : `Struct`
143 One-level-deep copy of this Struct.
144 """
145 return Struct(**self.getDict())
147 def __eq__(self, other: Any) -> bool:
148 return self.__dict__ == other.__dict__
150 def __len__(self) -> int:
151 return len(self.__dict__)
153 def __repr__(self) -> str:
154 itemsStr = "; ".join(f"{name}={val}" for name, val in self.getDict().items())
155 return f"{self.__class__.__name__}({itemsStr})"