Add algorithm to compute absolute age difference

[Ommodi07]

Describe your change:

Added an algorithm to calculate absolute age difference between two people.
Includes input validation and doctests.
Fixes #13489

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes Python #13489 ".

[ankit-nirala54]

#!/usr/bin/env python3
"""
age_diff.py

Calculate the absolute age difference between two people given their birthdates.

Functions:

• parse_date(value): parse and validate a date string (YYYY-MM-DD) or accept datetime.date.
• absolute_age_difference(d1, d2): return (years, months, days) difference, absolute value.

Run doctests:
python -m doctest age_diff.py -v
"""

from datetime import date, datetime, timedelta
from typing import Tuple, Union

DateLike = Union[str, date, datetime]

def parse_date(value: DateLike) -> date:
"""
Parse a date-like input into a datetime.date and validate it's not in the future.

Accepts:
  - 'YYYY-MM-DD' string
  - datetime.date
  - datetime.datetime

Raises:
  ValueError on invalid format or if the date is in the future.

Examples
--------
>>> parse_date("2000-01-15")
datetime.date(2000, 1, 15)
>>> # invalid format
>>> try:
...     parse_date("15-01-2000")
... except ValueError as e:
...     print("err")
err
"""
if isinstance(value, date) and not isinstance(value, datetime):
    d = value
elif isinstance(value, datetime):
    d = value.date()
elif isinstance(value, str):
    try:
        d = datetime.strptime(value, "%Y-%m-%d").date()
    except ValueError as exc:
        raise ValueError(f"Date string must be YYYY-MM-DD, got: {value!r}") from exc
else:
    raise ValueError(f"Unsupported date type: {type(value)}")

today = date.today()
if d > today:
    raise ValueError(f"Date {d.isoformat()} is in the future (today is {today.isoformat()}).")
return d

def _days_in_prev_month(ref: date) -> int:
"""
Helper: number of days in the month preceding the month of ref.
For example, if ref is 2020-03-05 -> returns days in Feb 2020 (29).
"""
first_of_month = ref.replace(day=1)
prev_last_day = first_of_month - timedelta(days=1)
return prev_last_day.day

def absolute_age_difference(d1: DateLike, d2: DateLike) -> Tuple[int, int, int]:
"""
Return the absolute difference between two dates as (years, months, days).

Rules:
  - years is the number of full years between the two dates
  - months is full months after removing years
  - days is remaining days after removing years and months

Examples
--------
Same day -> zero difference:
>>> absolute_age_difference("2000-01-01", "2000-01-01")
(0, 0, 0)

Simple difference:
>>> absolute_age_difference("1990-05-10", "1995-07-15")
(5, 2, 5)

Order doesn't matter (it's absolute):
>>> absolute_age_difference("1995-07-15", "1990-05-10")
(5, 2, 5)

Leap day handling (Feb 29):
>>> absolute_age_difference("2000-02-29", "2001-02-28")
(0, 11, 30)

Another leap example across many years:
>>> absolute_age_difference("1988-02-29", "2012-02-29")
(24, 0, 0)
"""
a = parse_date(d1)
b = parse_date(d2)

# Ensure a <= b
if a > b:
    a, b = b, a

# Start with year difference
years = b.year - a.year

# Adjust years if the last year is not yet a full year
if (b.month, b.day) < (a.month, a.day):
    years -= 1

# For months and days, compute an "anniversary" date after removing full years
# anniversary = a advanced by `year

[Ommodi07]

can you tell me in details what to do ?

…

On Sun, 19 Oct 2025 at 08:29, ankit-nirala54 ***@***.***> wrote: *ankit-nirala54* left a comment (TheAlgorithms/Python#13525) <#13525 (comment)> #!/usr/bin/env python3 """ age_diff.py Calculate the absolute age difference between two people given their birthdates. Functions: - parse_date(value): parse and validate a date string (YYYY-MM-DD) or accept datetime.date. - absolute_age_difference(d1, d2): return (years, months, days) difference, absolute value. Run doctests: python -m doctest age_diff.py -v """ from datetime import date, datetime, timedelta from typing import Tuple, Union DateLike = Union[str, date, datetime] def parse_date(value: DateLike) -> date: """ Parse a date-like input into a datetime.date and validate it's not in the future. Accepts: - 'YYYY-MM-DD' string - datetime.date - datetime.datetime Raises: ValueError on invalid format or if the date is in the future. Examples -------- >>> parse_date("2000-01-15") datetime.date(2000, 1, 15) >>> # invalid format >>> try: ... parse_date("15-01-2000") ... except ValueError as e: ... print("err") err """ if isinstance(value, date) and not isinstance(value, datetime): d = value elif isinstance(value, datetime): d = value.date() elif isinstance(value, str): try: d = datetime.strptime(value, "%Y-%m-%d").date() except ValueError as exc: raise ValueError(f"Date string must be YYYY-MM-DD, got: {value!r}") from exc else: raise ValueError(f"Unsupported date type: {type(value)}") today = date.today() if d > today: raise ValueError(f"Date {d.isoformat()} is in the future (today is {today.isoformat()}).") return d def _days_in_prev_month(ref: date) -> int: """ Helper: number of days in the month preceding the month of ref. For example, if ref is 2020-03-05 -> returns days in Feb 2020 (29). """ first_of_month = ref.replace(day=1) prev_last_day = first_of_month - timedelta(days=1) return prev_last_day.day def absolute_age_difference(d1: DateLike, d2: DateLike) -> Tuple[int, int, int]: """ Return the absolute difference between two dates as (years, months, days). Rules: - years is the number of full years between the two dates - months is full months after removing years - days is remaining days after removing years and months Examples -------- Same day -> zero difference: >>> absolute_age_difference("2000-01-01", "2000-01-01") (0, 0, 0) Simple difference: >>> absolute_age_difference("1990-05-10", "1995-07-15") (5, 2, 5) Order doesn't matter (it's absolute): >>> absolute_age_difference("1995-07-15", "1990-05-10") (5, 2, 5) Leap day handling (Feb 29): >>> absolute_age_difference("2000-02-29", "2001-02-28") (0, 11, 30) Another leap example across many years: >>> absolute_age_difference("1988-02-29", "2012-02-29") (24, 0, 0) """ a = parse_date(d1) b = parse_date(d2) # Ensure a <= b if a > b: a, b = b, a # Start with year difference years = b.year - a.year # Adjust years if the last year is not yet a full year if (b.month, b.day) < (a.month, a.day): years -= 1 # For months and days, compute an "anniversary" date after removing full years # anniversary = a advanced by `year — Reply to this email directly, view it on GitHub <#13525 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BCS6XV2CD7MJW5XPZJ6AEPT3YL5CFAVCNFSM6AAAAACJLB7WSGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTIMJZGE3DKNZRGA> . You are receiving this because you authored the thread.Message ID: ***@***.***>