Python mutable NamedTuple

Question

I am looking for a struct like data structure I can create multiple instances from and have some type hinting without being immutable.

So I have something like this:

class ConnectionConfig(NamedTuple):
    name: str
    url: str
    port: int
    user: str = ""
    pwd: str = ""
    client: Any = None

But I would like to have it mutable. I could do it like that:

class ConnectionConfig():
    def __init__(self, name: str, url: str, port: int, user: str = "", pwd: str = "", client: Any = None):
        self.name = name
        self.url = url
        self.port = port
        self.user = user
        self.pwd = pwd
        self.client = client

But man... that is ugly :/ Are there any built-in alternatives in python? (using Python 3.6.3)

You could use **kwargs and a (for) loop. And you could use eval (or exec) for this one. I'm just not sure about this because every time I use eval for assigning variables it throws an error. — user8179437
– user8179437, Commented Oct 21, 2017 at 18:08

viddik13 · Accepted Answer · 2017-10-27 00:27:52Z

3

Your implementation is quite the (only) built-in way to do it, actually:

class ConnectionConfig():
    def __init__(self, name: str, url: str, port: int, user: str = "",
                 pwd: str = "", client: Any = None):
        pass

Reading PEP 0484 I haven't found any other alternatives that fit your needs. Continuing the PEP chain, I guess this quote from PEP 20 The Zen of Python explains it:

There should be one-- and preferably only one --obvious way to do it.

answered Oct 27, 2017 at 0:27

viddik13

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Comments

gambuzzi · Accepted Answer · 2017-10-21 17:42:37Z

2

class ConnectionConfig():
    name: str
    url: str
    port: int
    user: str = ""
    pwd: str = ""
    client: Any = None
    def __init__(self, **kv):
        self.__dict__.update(kv)

then you can specify everything in the constructor

c=ConnectionConfig(port=22)

print (c.port)  # will print 22

answered Oct 21, 2017 at 17:42

gambuzzi

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2 Comments

Jodo Over a year ago

I actually already tried that one before. But the type hints are not working that way. I maybe didn't specify that in my question good enough.

viddik13 Over a year ago

The type hints will not work because they are not in the init

intellimath · Accepted Answer · 2021-08-01 11:34:17Z

There is a compact solution on the base of recordclass library:

> pip3 install recordclass

from recordclass import dataobject

class ConnectionConfig(dataobject):
    name: str
    url: str
    port: int
    user: str = ""
    pwd: str = ""
    client: Any = None

>>> con = ConnectionConfig('name','url',8080,'user','secret',tcp_client)

>>> sys.getsizeof(con)
108   # PyHEAD (16) + 6*sizeof(*void) bytes

If one want faster instance creation there is an option:

class ConnectionConfig(dataobject, fast_new=True):
    name: str
    url: str
    port: int
    user: str = ""
    pwd: str = ""
    client: Any = None

(Note: that this one could be less comfortable with IDE editor's autocompletion)

Another option:

>>> from recordclass import make_dataclass
>>> ConnectionConfig = make_dataclass(
          "ConnectionConfig",
          [('name',str), ('url',str), ('port',str), 
           ('use',str), ('pwd',str), ('client',Any)],
          defaults=(None,), 
          fast_new=True)

maor10 · Accepted Answer · 2017-10-21 18:18:51Z

0

How about using recordclass (pip install recordclass)?

from recordclass import recordclass


>>> Point = recordclass('Point', 'x y')

>>> p = Point(3, 2)
>>> p
Point(x=3, y=2)
>>> p.x = 8

It's (nearly) the same api as namedtuple and it's mutable

answered Oct 21, 2017 at 18:18

maor10

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4 Comments

Jodo Over a year ago

I would prefer sth built in. Nevertheless, I also don't see how type hinting can be used.

maor10 Over a year ago

Are you sure this doesn't work with your IDE? ipython knows to autocomplete with recordclass

Jodo Over a year ago

I never said it does not work. But again, how can I use type hints with recordclass. As I see it, that does not work.

intellimath Over a year ago

Jodo: recordclass already support typehints:: from recordclass import RecordClass from typing import Any class ConnectionConfig(RecordClass): name: str url: str port: int user: str = "" pwd: str = "" client: Any = None >>> cf = ConnectionConfig('name', 'example.com', 8080, 'qwerty', None) >>> print(cf.name, cf.url, cf.port, cf.pwd, repr(cf.client)) name example.com 8080 None None

Jodo · Accepted Answer · 2017-10-28 15:26:02Z

0

Calling "_asdict()" on creation of the NamedTuple will transform it to an OrderedDict(), but not really satisfying at all...

from typing import NamedTuple

class ConnectionConfig(NamedTuple):
    name: str
    url: str
    port: int
    user: str = ""
    pwd: str = ""

mutable_connection_cfg = ConnectionConfig("my_name", "my_url", 111, "my_user", "my_pwd")._asdict()

print(mutable_connection_cfg)
>> OrderedDict([('name', 'my_name'), ('url', 'my_url'), ('port', 111), ('user', 'my_user'), ('pwd', 'my_pwd')])

edited Oct 28, 2017 at 15:26

answered Oct 28, 2017 at 7:51

Jodo

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Comments

David · Accepted Answer · 2022-08-26 07:46:08Z

0

You can use the pass statement.

class myclass: pass

Then you can create the attributes just before using them:

myclass.a=0
myclass.b='string'

answered Aug 26, 2022 at 7:46

David

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1 Comment

Keith Over a year ago

If you're going this route, a cleaner way is to use SimpleNamespace.

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