How to detect if dates are consecutive in Python?

Question

I have an access table with a 'Date' field. it has random dates for each record. I've built a script to append all the records into a list and then set the list to filter out only the unique values:

dateList = []
# cursor search through each record and append all records in the date 
# field to a python list
for row in rows:
   dateList.append(row.getValue("DATE_OBSERVATION").strftime('%m-%d-%Y'))

# Filter unique values to a set
newList = list(set(dateList))

This returns (on my test table):

['07-06-2010', '06-24-2010', '07-05-2010', '06-25-2010']

Now that I have the unique values for the "DATE_OBSERVATION" field, I want to detect if:

• the dates are single (i.e. only one unique date is returned because that is the date in every record)
• if the dates are a range of dates (i.e. all of the dates fall into a consecutive range)
• if the dates are multiple dates, but are not in a range of consecutive dates

Any suggestions would be much appreciated! Mike

Answer 1

Rather than rolling your own consecutive function you can simply convert date objects to integers using the .toordinal() method of datetime objects. The difference between the maximum and minimum value of the set of ordinal dates is one more than the length of the set:

from datetime import datetime

date_strs = ['07-06-2010', '06-24-2010', '07-05-2010', '06-25-2010']
# date_strs = ['02-29-2012', '02-28-2012', '03-01-2012']
# date_strs = ['01-01-2000']
dates = [datetime.strptime(d, "%m-%d-%Y") for d in date_strs]

date_ints = set([d.toordinal() for d in dates])

if len(date_ints) == 1:
    print "unique"
elif max(date_ints) - min(date_ints) == len(date_ints) - 1:
    print "consecutive"
else:
    print "not consecutive"