Adding months to a date based on a comparison where dateutil.relativedelta is greater than a specifi-CodePudding

My goal is to add a specified amount of months to a start_date based on the length of the time period between start_date and end_date. If the period lasted more than 10 years, 3 months should be added, otherwise 1 month. The calculation has to be precise and should be able to account for the specific numbers of days in a given month, as well as for leap years. I tried to accomplish this by using dateutil.relativedelta like so:

from dateutil.relativedelta import relativedelta
from dateutil import parser

# Extract date from string
start_date = parser.parse("2050-11-01")
end_date = parser.parse("1980-11-01")

# Calculate difference
delta = relativedelta(start_date, end_date)
print(delta)

if delta > relativedelta(years= 10):
    new_end_date = start_date   relativedelta(months=3)
else:
   new_end_date = start_date   relativedelta(months=1)

print(new_end_date)

However, this gives the following output:

relativedelta(years= 70)
TypeError: '>' not supported between instances of 'relativedelta' and 'relativedelta'

Searching for the error on SO made it clear that there is no simple way to compare dateutil.relativedelta. Does anyone know of a work-around for my use case?

CodePudding user response：

Here's my suggestion:

Set the (relative) period you are testing against (10 years)
Add it to the earliest input date
Check if that new date is earlier than the latest input date

This way, you still get the relative-ness of the relativedelta, but you get two hard dates to compare:

from dateutil.relativedelta import relativedelta
from dateutil import parser

# Extract date from string
start_date = parser.parse("2050-11-01")
end_date = parser.parse("1980-11-01")

# Set the size of the period
period = relativedelta(years=10)

# Test if adding the period to the earliest date makes it surpass the latest date
if min(start_date, end_date)   period <= max(start_date, end_date):
    new_end_date = start_date   relativedelta(months=3)
else:
   new_end_date = start_date   relativedelta(months=1)

print(new_end_date)
# 2051-02-01 00:00:00

In this case, start & end do not imply earlier & later, so you have to do the min and max operations.