Why does beancount.core.data.Posting require an amount?

[Aaron Stacy]

This ledger is valid even though the amount for the second posting of the transaction is omitted:

2024-01-01 open Assets:Checking
2024-01-01 open Expenses:Groceries

2024-01-01 * "Groceries"
  Expenses:Groceries 10 USD
  Assets:Checking

But Beancount's core data type for Posting requires a non-None amount for the units field, even though it's not a runtime error to pass None into it (example repro). I also notice, the beancount.loader module will insert an Amount when loading the Python objects. 

I can see why this might be desirable for code maintenance, but it seems to constrain the ledger unnecessarily. My question is should Posting#units have the type Optional[Amount]? I'd be happy to mail a pull request.

The background is that I upgraded to v3; I really love the nice static typing, but I've got a h̴e̴r̴d̴ ̴o̴f̴ ̴f̴e̴r̴a̴l̴ ̴c̴a̴t̴s̴ handful of scripts for importing transactions, and those create Posting objects to be output with beancount.parser.printer, and for that I prefer the cleaner ledger syntax of omitting the second posting's amount.

[Daniele Nicolodi]

On 20/05/24 15:24, Aaron Stacy wrote:
> But Beancount's core data type for Posting requires a non-None amount
> for the units field

It is an error in the typing annotation. Feel free to send a PR.

> I also notice, the beancount.loader module will insert an Amount when loading the Python objects.

This is because beancount.loader also runs the plugins and does booking.
This requires the transactions to be completed, namely amounts for all
postings must be inferred. If you don't what that, you can load a ledger
into a Python data structure with beancount.parser.parse_file()

Cheers,
Dan

[Aaron Stacy]

On Mon, May 20, 2024 at 4:08 PM Daniele Nicolodi <dan...@grinta.net> wrote:

On 20/05/24 15:24, Aaron Stacy wrote:
> But Beancount's core data type for Posting requires a non-None amount
> for the units field

It is an error in the typing annotation. Feel free to send a PR.

Ah right on. Sent 

https://github.com/beancount/beancount/pull/825

> I also notice, the beancount.loader module will insert an Amount when loading the Python objects.

This is because beancount.loader also runs the plugins and does booking.
This requires the transactions to be completed, namely amounts for all
postings must be inferred. If you don't what that, you can load a ledger
into a Python data structure with beancount.parser.parse_file()

Aaaah that makes sense. Thanks for the pointer!

Cheers,
Dan

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