Make a list of list where dates are chained together based on their delta

periodize_dates.py

def periodize_dates(dates:list=[], delta:datetime.timedelta=timedelta(days=14), dateformat='%Y-%m-%d'):
    """
    Takes a list of dates and returns a list of lists, where the original list has been divided into strings of dates that are within the provided delta.
    
    Parameters:
    dates (list): List of dates that you want periodized.
    delta (datetime.timedelta/int): The delta that you want compared. If provided as type `int`, the value will be interpreted as `timedelta.days=<int>`.
    dateformat (str): A date formatting string that all dates in the list will need to adhere to.
    Returns:
    list:Periodized dates
    """

    try:
        dates = sorted([datetime.datetime.strptime(x, dateformat) for x in dates])
    except ValueError as e:
        date = re.search(r'''['"](.*)['"] does not match format''', str(e))
        if date:
            date = date.groups()[0]
        raise ValueError(f'A date found in list that did not adhere to format (`{date}`). Needs to follow format `{dateformat}`.') from None

    if isinstance(delta, int):
        delta = timedelta(days=delta)

    periods = []

    for ix, date in enumerate(dates):
        min_date = date - delta
        max_date = date + delta

        prev_date, next_date = None, None
        start_chain, end_chain, in_chain, solo_date = None, None, None, None
        prev_date_in_range, next_date_in_range = None, None

        try:
            if ix-1 >= 0:
                prev_date = dates[ix-1]
        except IndexError:
            prev_date = None

        try:
            next_date = dates[ix+1]
        except IndexError:
            next_date = None

        if next_date:
            next_date_in_range = next_date >= min_date and next_date <= max_date

        if prev_date:
            prev_date_in_range = prev_date >= min_date and prev_date <= max_date

        if all([next_date, prev_date, prev_date_in_range, next_date_in_range]):
            # In the loop and in a chain (near previous date and next)
            in_chain = True
        elif all([next_date, prev_date, next_date_in_range]) and not prev_date_in_range:
            # In the loop and beginning of a chain (not near previous date but near next)
            start_chain = True
        elif all([next_date, prev_date, prev_date_in_range]) and not next_date_in_range:
            # In the loop and end of a chain (near previous date but not next)
            end_chain = True
        elif all([next_date, prev_date]) and not all([prev_date_in_range, next_date_in_range]):
            # In the loop but solo date (not not near previous date nor next)
            solo_date = True
        elif next_date and next_date_in_range:
            # In the loop but solo date (not not near previous date nor next)
            start_chain = True
        elif next_date:
            solo_date = True
        elif prev_date and prev_date_in_range:
            end_chain = True
        elif prev_date:
            solo_date = True
        elif not next_date and not prev_date:
            solo_date = True
        else:
            raise RuntimeError('An unexpected error occurred.')

        if start_chain:
            periods.append([date])

        elif end_chain:
            periods[len(periods)-1].append(date)

        elif solo_date:
            periods.append([date])

        elif in_chain:
            periods[len(periods)-1].append(date)
            
    return periods