leap_year_date.py

import datetime
from datetime import date

def add_year(date_obj):
  try:
    new_date_obj = date_obj.replace(year = date_obj.year + 1)
  except ValueError:
    # This gets executed when the above method fails, 
    # which means that we're making a Leap Year calculation
    new_date_obj = date_obj.replace(year = date_obj.year + 4)
  return new_date_obj

def next_date(date_string):
  # Convert the argument from string to date object
  date_obj = datetime.datetime.strptime(date_string, r"%Y-%m-%d")
  next_date_obj = add_year(date_obj)

  # Convert the datetime object to string, 
  # in the format of "yyyy-mm-dd"
  next_date_string = next_date_obj.strftime("%Y-%m-%d")
  return next_date_string

today = date.today()  # Get today's date
print(next_date(str(today))) 
# Should return a year from today, unless today is Leap Day

print(next_date("2021-01-01")) # Should return 2022-01-01
print(next_date("2020-02-29")) # Should return 2024-02-29