Convert date to day of year without using datetime

Question

I have to return the day of the year (int) for a given string date (eg "September, 14, 2019" ) WITHOUT using datetime . I also have to make it basic enough to where I can make two other similar functions for different calendars.

---

This is what I had before:

def date_to_day_of_year(self, month, day, year):
  '''
  Given the month, day and year of a date,
  return the number of the day in the year.
  '''
  day_of_year = 0
  for month_name, days_in_month in month_days.items():
      if month_name == month:
          break
      day_of_year += days_in_month
  day_of_year += day
  if self.is_leap_year(year) and ((month != 'Feb') and (month != 'Jan')):
      day_of_year += 1
  return day_of_year(month, day, year)

---

But I just can't seem to convert it into this:

def day_of_year_to_date(self, day_of_year, year):
  '''
  Convert day of year to date.
  '''
  # ...

Answer 1

This should achieve the desired effect. I'm making a few assumptions since you didn't specify output format or input data.

def day_of_year_to_date(day_of_year, year):
    sum_of_days = 0
    for month_name, days_in_month in month_days.items():
        sum_of_days += days_in_month
        if sum_of_days > day_of_year:
            month = month_name
            day = str(days_in_month - sum_of_days%day_of_year)
            break
        else:
            pass
    return month+', '+day+' '+str(year)

day_of_year = 110
year = 2020
day_of_year_to_date(day_of_year, year)

#'April, 10 2020'

I'm making the simple assumption that each month is 30 days -- you're dictionary should be accurate to the month and year (and obviously doesn't require datetime to generate).

import datetime 
month_days = {}
for i in range(1,13):
    month_days[datetime.date(2008, i, 1).strftime('%B')] = 30
    
month_days

###
{'January': 30,
 'February': 30,
 'March': 30,
 'April': 30,
 'May': 30,
 'June': 30,
 'July': 30,
 'August': 30,
 'September': 30,
 'October': 30,
 'November': 30,
 'December': 30}

Answer 2

First you will need some data structure to hold the number of days in each month like so:

month_data = [(1, “January”, 31), (2, “February”, 28), ... (12,”December”,31)]

Then you can do some modification for leap years :

if isLeapYear(year):
    month_data[1][2] = 29

Then you can create a counter to track the month of the year :

month_of_year = 0

Then you can iterate over your month data subtracting the number of days in each month from your day_of_year variable. The leftover amount will represent the day of the month :

for month in month_data:
    if month[2] < day_of_year:
        day_of_year -= month[2]
        month_of_year ++
day_of_month = day_of_year

Once you have the month of the year , and the day of the month it should be simple to return a string that represents the full date.

Of course you will have to do some error checking to make sure that the input is valid 0<day_of_year<365 or 366 if leap year. But I hope this helps!