Re: [Quantlib-dev] High_resolution_date subtracting

[Klaus S. <kl...@sp...>]

Hi

maybe the following function is of help, which adds a fraction of a year to a date.

def plusDt(date, dt):
    return ql.Date(date.dayOfMonth(), date.month(), date.year(),
                   date.hours(), date.minutes(), 
                   date.seconds() + round(dt*365*24*60*60),
                   date.milliseconds(), date.microseconds())

This function returns the following dates

plusDt(ql.Date(1,1, 2019), 1) 
--> 2020-01-01T00:00:00,000000

plusDt(ql.Date(1,1, 2019), 1.0/365.0)  
--> 2019-01-02T00:00:00,000000

print(plusDt(ql.Date(1,1, 2019), 0.5/365.0)) 
--> 2019-01-01T12:00:00,000000

For the reverse operation (or subtracting two date time stamps) IMO you can use 
ql.Actual365Fixed().yearFraction(date1, date2), e.g. 

ql.Actual365Fixed().yearFraction(
    ql.Date(1,1,2019), plusDt(ql.Date(1,1,2019),0.5/365.))
--> 0.001369863

best regards
Klaus