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From: Thomas Passin <list1@tompassin.net>
Newsgroups: comp.lang.python
Subject: Re: Dynamic classes
Date: Mon, 19 May 2025 18:11:20 -0400
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On 5/19/2025 5:49 PM, Mats Wichmann via Python-list wrote:
> On 5/19/25 09:51, Jonathan Gossage via Python-list wrote:
>> I have created a dynamic class using the type() function:
>> x = type('MyFlags', (), {'Flag1': 1, 'Flag2': 2, 'Flag3: 4, ' 
>> '__init__' :
>> __init__})
>> The new class is there, and the class variables, Flag1, Flag2, and Flag3,
>> are present correctly. However, when I try to create an instance of this
>> class with the following code:
>> y = x('Flag1', 'Flag2')
>> it fails with a TypeError stating that 'MyFlags' does not accept 
>> arguments.
>> What do I have to do to make this happen?. BTW __init__(self, *args) is
>> defined as the instance initializer.
> 
> Might help if you show the init function. I've done something similar to 
> this without trouble, but not using the unpacking (i.e. *args). I used 
> this in an ancient blog post (thus, pre-typing, and such):
> 
> def transact(acct, amount):
>      acct.balance += amount
> 
> def pay_interest(acct):
>      acct.balance += acct.balance * acct.interest_rate
> 
> def account_init(acct, num, name, bal, rate):
>      acct.acct_number = num
>      acct.acct_holder = name
>      acct.balance = bal
>      acct.interest_rate = rate
> 
> account = {
>      "acct_number": "XXX",
>      "acct_holder": "",
>      "balance": 0.0,
>      "interest_rate": 0.0,
>      "transact": transact,
>      "pay_interest": pay_interest,
>      "__init__": account_init,
> }
> 
> AccountType = type("AccountType", (), account)
> 
> myaccount = AccountType("1234567", "J. Q. Public", 20.0, 0.01)
> print(myaccount.balance)
> myaccount.transact(-10)
> print(myaccount.balance)
> myaccount.pay_interest()
> print(myaccount.balance)
> 

It's interesting that in Jython there is a way to do something 
conceptually similar to turn a Jython class into a Java class.  Here's 
one of mine:

synchronized CoordinatorType getCoord() {
     JythonObjectFactory factory = new JythonObjectFactory (
         // Type class, Jython module name, class name
         CoordinatorType.class, "Coordinator", "Coordinator");

     // Java class
     CoordinatorType coord = (CoordinatorType) factory.createObject();
     return coord;
}

// Instantiate a Coordinator
// Error handling elided for clarity
CoordinatorType c;
c = getCoord();