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First solution in Clear category for Unlucky Days by mz97
import calendar
import datetime
def checkio(year):
result = 0
if calendar.isleap(year): dd=366
else: dd=365
d = datetime.date(year,1,1)
for i in range(0,dd):
if d.isoweekday()==5 and d.day==13: result+=1
d += datetime.timedelta(days=1)
return result
Oct. 28, 2016