Changing a string with dates into days after Jan. 1, 2010

For the function below, I am inputting a string like "6/29/2020" and "8/10/2010" and I want to get a numbers of days after Jan. 1, 2010. For example, if I input "1/29/2010", I want the integer 29 to be returned.

Currently, I have gotten "6/29/2020" to a string "2020-06-29". Now I just need help with converting that string into the days after Jan. 1, 2010.

I feel like I have posted everything needed for you to help, but if you need more information, let me know. Thank You for helping me with this problem.

def day_conversion(dates):
  import datetime
  
  i = 0

  for day in dates:
        day = day.split('/')

        if len(day[0]) == 1:
              day[0] = f"0{day[0]}"
        if len(day[1]) == 1:
              day[1] = f"0{day[1]}"

        day = f"{day[2]}-{day[0]}-{day[1]}"

      #   day = date.format(day)
      #   from datetime import date
      #   day0 = date(2000, 1, 1)
      #   day = day - day0
        
        dates[i] = day
        i += 1

  return dates

>Solution :

datetime has a function for parsing dates, and subtracting two datetime objects gives a timedelta object with a .days attribute:

from datetime import datetime

def days_since_jan1_2010(date):
    dt = datetime.strptime(date, '%m/%d/%Y')
    diff = dt - datetime(2010, 1, 1)
    return diff.days

def day_conversion(dates):
    return [days_since_jan1_2010(d) for d in dates]

print(day_conversion(['6/29/2020', '8/10/2010', '1/1/2010', '1/2/2010']))

Output:

[3832, 221, 0, 1]