relativedelta in python when working in months

python, relativedelta

Solution

`relativedelta(months=12)` is actually `relativedelta(years=+1)` It automatically converts months to years. For example `months=13` would result in `relativedelta(years=+1, months=+1)`

Further, years only change when months go below -11 or above 11. So if the amount of `months` after the operation is still between -11 and 11, the year will not change.

The solution would be that you need to look at both the `rdelta.years` and `rdelta.months` values to get the "net months" you're looking for.

def total_months(rdelta):
    return (rdelta.years * 12) + rdelta.months

You could subclass `relativedelta` to make this a bit more intuitive for your use.

class reldelta(relativedelta):
    @property
    def total_months(self):
        return (self.years * 12) + self.months

Then

>>> delta = reldelta(years=1) - relativedelta(months=4)
>>> delta
reldelta(years=+1, months=-4)
>>> delta.total_months
8

Of course, this can get messy if you want to try to factor in days to this, because the number of days in a month changes. This is why `days` are not bounded like months are

>>> relativedelta(days=9999)
relativedelta(days=+9999)

Problem

Suppose I am working with relative delta when it comes to months. The problem is when I do: ``` x = relativedelta(months=12) x.months > 0 ``` This is a problem when I try to do something like this: ``` y = relativedelta(months=12) - relativedelta(months=4) y > relativedelta(years=+1, months=-4) y.months > -4 ``` I was hoping for a months value of 8 (12 - 4). Anyone know how to best approach this so I can achieve the output I am looking for?

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