|
| 1 | +--- |
| 2 | +Title: 'total_ordering()' |
| 3 | +Description: 'Generates missing comparison methods in a class based on a minimal set of defined ones.' |
| 4 | +Subjects: |
| 5 | + - 'Code Foundations' |
| 6 | + - 'Computer Science' |
| 7 | +Tags: |
| 8 | + - 'Classes' |
| 9 | + - 'Modules' |
| 10 | + - 'Python' |
| 11 | +CatalogContent: |
| 12 | + - 'learn-python-3' |
| 13 | + - 'paths/computer-science' |
| 14 | +--- |
| 15 | + |
| 16 | +In Python, the **`total_ordering()`** decorator from the `functools` module simplifies the creation of fully ordered classes. By defining the `__eq__()` method and one additional comparison method (`__lt__()`, `__le__()`, `__gt__()`, or `__ge__()`), all other rich comparison methods are automatically generated. |
| 17 | + |
| 18 | +This decorator reduces redundant code in custom classes that require complete ordering behavior for comparisons, sorting, and equality checks. |
| 19 | + |
| 20 | +## Syntax |
| 21 | + |
| 22 | +```pseudo |
| 23 | +from functools import total_ordering |
| 24 | +
|
| 25 | +@total_ordering |
| 26 | +class ClassName: |
| 27 | + def __eq__(self, other): ... |
| 28 | + def __lt__(self, other): ... |
| 29 | +``` |
| 30 | + |
| 31 | +**Parameters:** |
| 32 | + |
| 33 | +The `total_ordering()` decorator takes no parameters. |
| 34 | + |
| 35 | +**Return value:** |
| 36 | + |
| 37 | +Returns a class with the missing comparison methods (`__le__`, `__gt__`, and `__ge__`) automatically added. |
| 38 | + |
| 39 | +## Example 1: Numeric Wrapper Class |
| 40 | + |
| 41 | +The following example defines a class that compares wrapped numeric values. Only `__eq__()` and `__lt__()` are implemented; the rest are generated automatically: |
| 42 | + |
| 43 | +```py |
| 44 | +from functools import total_ordering |
| 45 | + |
| 46 | +@total_ordering |
| 47 | +class Number: |
| 48 | + def __init__(self, value): |
| 49 | + self.value = value |
| 50 | + |
| 51 | + def __eq__(self, other): |
| 52 | + return self.value == other.value |
| 53 | + |
| 54 | + def __lt__(self, other): |
| 55 | + return self.value < other.value |
| 56 | + |
| 57 | +print(Number(3) < Number(4)) |
| 58 | +print(Number(5) >= Number(5)) |
| 59 | +print(Number(7) > Number(1)) |
| 60 | +``` |
| 61 | + |
| 62 | +The outout of this code is: |
| 63 | + |
| 64 | +```shell |
| 65 | +True |
| 66 | +True |
| 67 | +True |
| 68 | +``` |
| 69 | + |
| 70 | +## Example 2: Ordering Strings by Length |
| 71 | + |
| 72 | +This example demonstrates ordering based on string length instead of direct string comparison: |
| 73 | + |
| 74 | +```py |
| 75 | +from functools import total_ordering |
| 76 | + |
| 77 | +@total_ordering |
| 78 | +class Word: |
| 79 | + def __init__(self, text): |
| 80 | + self.text = text |
| 81 | + |
| 82 | + def __eq__(self, other): |
| 83 | + return len(self.text) == len(other.text) |
| 84 | + |
| 85 | + def __lt__(self, other): |
| 86 | + return len(self.text) < len(other.text) |
| 87 | + |
| 88 | +print(Word("apple") < Word("banana")) |
| 89 | +print(Word("kiwi") == Word("pear")) |
| 90 | +print(Word("grape") > Word("fig")) |
| 91 | +``` |
| 92 | + |
| 93 | +The output of this code is: |
| 94 | + |
| 95 | +```shell |
| 96 | +True |
| 97 | +True |
| 98 | +True |
| 99 | +``` |
| 100 | + |
| 101 | +## Codebyte Example: Prioritizing Tasks |
| 102 | + |
| 103 | +The following codebyte defines a class where objects are ordered by priority value: |
| 104 | + |
| 105 | +```codebyte/python |
| 106 | +from functools import total_ordering |
| 107 | +
|
| 108 | +@total_ordering |
| 109 | +class Task: |
| 110 | + def __init__(self, name, priority): |
| 111 | + self.name = name |
| 112 | + self.priority = priority |
| 113 | +
|
| 114 | + def __eq__(self, other): |
| 115 | + return self.priority == other.priority |
| 116 | +
|
| 117 | + def __lt__(self, other): |
| 118 | + return self.priority > other.priority |
| 119 | +
|
| 120 | +tasks = [ |
| 121 | + Task("Write report", 2), |
| 122 | + Task("Fix bugs", 5), |
| 123 | + Task("Plan sprint", 3) |
| 124 | +] |
| 125 | +
|
| 126 | +tasks.sort() |
| 127 | +for t in tasks: |
| 128 | + print(t.name, t.priority) |
| 129 | +``` |
| 130 | + |
| 131 | +Higher priority numbers are treated as greater for sorting purposes. |
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