title: Python Timedelta Arithmetic With noleap Calendars
body: <p>I'm working with CMIP5 data that has time units of "days since 1-1-1850". To find the current day I'm working with in the file, I would normally just do a timedelta addition from 1-1-1850 and the time value (in days) for the datapoint that I'm working with. However, CMIP5 (or at least the file I'm using) uses a 'noleap' calendar, meaning that all years are only 365 days. </p>
  
  <p>In my current case, when dealing with the datapoint that corresponds to January 1, 1980, I add its time argument of 47450 days to the original date of January 1, 1850. However, I get back an answer of December 1, 1979 because all the Feb. 29ths between 1850 and 1980 are excluded. Is there an additional argument in timedelta or datetime in general that deals with calendars that exclude leap days?</p>