Subtract n months from datetime [Why?]

[Paulo da Silva]

Às 20:25 de 22/06/22, Barry Scott escreveu:
> 
> 
>> On 22 Jun 2022, at 17:59, Paulo da Silva <p_d_a_s_i_l_v_a_ns at nonetnoaddress.pt> wrote:
>>
>> Às 05:29 de 21/06/22, Paulo da Silva escreveu:
>>
>> As a general response to some comments ...
>>
>> Suppose we need to delete records from a database older than ...
>> Today, it's usual to specify days. For example you have to keep some gov papers for 90 days. This seems to come from computers era. In our minds, however, we immediately think 90 days=3 months.
>> For example, one may want to delete some files older than 9 months. It's far more intuitive than 270 days.
>> When we talk about years it is still going. For example I need to keep my receipts for 5 years because IRS audits.
>> Accepting this, it's intuitive, for example, that 3 months before July, 31 is April, 30.
>> The same happens for the years. 5 years before February, 29 is February, 28.
> 
> The advantage of 30 days, 90 days etc is that a contract or law does not need to tell you
> how to deal with the problems of calendar months.
> 
> As you say in peoples thoughts that 1 month or 3 months etc. But an accounts department
> will know how to to the number of days till they have to pay up.
> 
Yes. But my point is to justify why I want months. And it depends on the 
application.
Let's suppose a program for Joe User to clean something - files, for 
example. There are no rules except for the comfort of the user. He would 
prefer to be able to say 9 months back instead of 270 days. And by 9 
months, he expects to count down 9 months. Not 270 days.
That's what happens with the script I am writing.

Paulo