Subtract n months from datetime [Why?]

[MRAB]

On 2022-06-22 20:25, Barry Scott wrote:
> 
> 
>> 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.
> 
OT, but in the UK, when the Gregorian Calendar was adopted, there were 
complaints.

It's often believed that they were just being superstitious about 
"losing" 11 days, but the truth is that they were complaining that rent 
was paid by the month, but wages by the number of days worked.

That month was a lot shorter, with far fewer working days, yet they were 
still expected to pay the same rent!