内容简介:By John Lekberg on June 06, 2020.This week's post is about using
Using enumerated types in Python
By John Lekberg on June 06, 2020.
This week's post is about using enumerated types (enums) in Python. You will learn:
- How to use enums to manage data that takes on a finite set of states.
- How to impose a custom ordering on data.
-
How to represent a combination of states using
Flag
andIntFlag
.
What are enums?
Enumerated types (enums) are sets of unique values. E.g. A tier list , with S-tier being the best, followed by A, B, C, D, and F:
import enum Tier = enum.IntEnum("Tier", ["S", "A", "B", "C", "D", "F"]) list(Tier)
[<Tier.S: 1>, <Tier.A: 2>, <Tier.B: 3>, <Tier.C: 4>, <Tier.D: 5>, <Tier.F: 6>]
Tier.S < Tier.C
True
sorted([Tier.B, Tier.D, Tier.S, Tier.A, Tier.F, Tier.C])
[<Tier.S: 1>, <Tier.A: 2>, <Tier.B: 3>, <Tier.C: 4>, <Tier.D: 5>, <Tier.F: 6>]
In this case, using an IntEnum object is easier than using a string because the tiers compare correctly:
Tier.S < Tier.C
True
"S" < "C"
False
sorted([Tier.B, Tier.D, Tier.S, Tier.A, Tier.F, Tier.C])
[<Tier.S: 1>, <Tier.A: 2>, <Tier.B: 3>, <Tier.C: 4>, <Tier.D: 5>, <Tier.F: 6>]
sorted(["B", "D", "S", "A", "F", "C"])
['A', 'B', 'C', 'D', 'F', 'S']
And spelling mistakes are caught:
Tier.Z < Tier.Q
AttributeError: Z
"Z" < "Q"
False
Using an IntEnum
object is easier than using an int
because the IntEnum
allows you to write mnemonics
for the values:
Tier.S < Tier.C
True
1 < 4
True
sorted([Tier.B, Tier.D, Tier.S, Tier.A, Tier.F, Tier.C])
[<Tier.S: 1>, <Tier.A: 2>, <Tier.B: 3>, <Tier.C: 4>, <Tier.D: 5>, <Tier.F: 6>]
sorted([3, 5, 1, 2, 6, 4])
[1, 2, 3, 4, 5, 6]
When should I use enums?
I use enums when:
- The data that I'm working with has a small number of states (e.g. "pass" or "fail").
- The data has an ordering that doesn't work with strings (e.g. "S" before "A" in a tier list).
- The data can be represented as a set of boolean flags (e.g. the flag register of a Zilog Z80 microprocessor ).
Here's code for each of these examples:
import random import collections Test = enum.Enum("Test", ["Pass", "Fail"]) row = lambda: [ random.choice(list(Test)), random.choice(["Bobby", "Linda", "John"]) ] data = [ row() for _ in range(10) ] data
[[<Test.Pass: 1>, 'John'], [<Test.Pass: 1>, 'Bobby'], [<Test.Fail: 2>, 'Linda'], [<Test.Fail: 2>, 'Bobby'], [<Test.Pass: 1>, 'Linda'], [<Test.Pass: 1>, 'Bobby'], [<Test.Pass: 1>, 'Linda'], [<Test.Pass: 1>, 'Bobby'], [<Test.Pass: 1>, 'Bobby'], [<Test.Pass: 1>, 'Bobby']]
[ student for test, student in data if test == Test.Fail ]
['Linda', 'Bobby']
import random import collections Tier = enum.IntEnum("Tier", ["S", "A", "B", "C", "D", "F"]) data_tiers = random.choices(list(Tier), k=9) data_names = ["Mario", "Link", "Samus", "Yoshi", "Kirby", "Fox", "Pikachu", "Ness", "Luigi"] data = list(zip(data_tiers, data_names)) data
[(<Tier.B: 3>, 'Mario'), (<Tier.A: 2>, 'Link'), (<Tier.F: 6>, 'Samus'), (<Tier.B: 3>, 'Yoshi'), (<Tier.C: 4>, 'Kirby'), (<Tier.D: 5>, 'Fox'), (<Tier.A: 2>, 'Pikachu'), (<Tier.S: 1>, 'Ness'), (<Tier.A: 2>, 'Luigi')]
rankings = collections.defaultdict(set) for tier, name in data: rankings[tier].add(name) for tier in Tier: names = sorted(rankings[tier]) print(f"{tier.name}-tier: {', '.join(names)}")
S-tier: Ness A-tier: Link, Luigi, Pikachu B-tier: Mario, Yoshi C-tier: Kirby D-tier: Fox F-tier: Samus
import random state = 0 for flag in Z80_Flag: # 50% chance that p is True. p = random.random() < 0.5 if p: state |= flag state
<Z80_Flag.Sign|Parity_Overflow|Subtract: 134>
for flag in Z80_Flag: if state & flag: status = "#" else: status = "." print(f"{flag.name:16} {status}")
Carry . Subtract # Parity_Overflow # Half_Carry . Zero . Sign #
Python's support for enums
Python supports four different types of enums via the enum module:
Enum IntEnum IntFlag Flag
What are the differences between these four?
Enum
and Flag
do not mix with integers. IntEnum
and IntFlag
do mix with integers.
import enum Test = enum.Enum("Test", ["Pass", "Fail"]) IntTest = enum.IntEnum("IntTest", ["Pass", "Fail"]) Test.Pass + 0
TypeError: unsupported operand type(s) for +: 'Test' and 'int'
IntTest.Pass + 0
Z80 = enum.Flag("Z80", ["Carry", "Subtract", "Parity", "Zero"]) IntZ80 = enum.IntFlag("IntZ80", ["Carry", "Subtract", "Parity", "Zero"]) Z80.Carry | 2
TypeError: unsupported operand type(s) for |: 'Z80' and 'int'
IntZ80.Carry | 2
<IntZ80.Subtract|Carry: 3>
Enum
and IntEnum
represent states that can't be combined. Flag
and IntFlag
represent states that can be combined.
Test = enum.Enum("Test", ["Pass", "Fail"]) Z80 = enum.Flag("Z80", ["Carry", "Subtract", "Parity", "Zero"]) Test.Pass | Test.Fail
TypeError: unsupported operand type(s) for |: 'Test' and 'Test'
Z80.Carry | Z80.Zero
<Z80.Zero|Carry: 9>
In conclusion...
In this week's post you learned how to use enums to manage data that takes on a
finite set of states.
Enums allow you to impose a custom ordering on data and represent a combination
of states using Flag
and IntFlag
.
My challenge to you:
Create an IntFlag
that represents the input status of a standard NES
controller
.
If you enjoyed this week's post, share it with your friends and stay tuned for next week's post. See you then!
以上所述就是小编给大家介绍的《Using Enumerated Types in Python》,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对 码农网 的支持!
猜你喜欢:本站部分资源来源于网络,本站转载出于传递更多信息之目的,版权归原作者或者来源机构所有,如转载稿涉及版权问题,请联系我们。
HTML 压缩/解压工具
在线压缩/解压 HTML 代码
JS 压缩/解压工具
在线压缩/解压 JS 代码