Extend a pandas datetime index

extend_datetime.py

import pandas as pd


def extend_datetime_index(index: pd.DatetimeIndex, end: pd.Timestamp = None, periods: int = None) -> pd.DatetimeIndex:
    """
    Minimal function for extending a pandas DateTimeIndex.
    Original attributes of the `index` (e.g name or tz) are not kept.
    Only the `freq` attribute is preserved.
    """
    if (bool(end) == bool(periods)): # xor
        msg = "Of the 2 parameters, `end` and `periods`, exactly 1 must be specified."
        raise ValueError(msg)
    
    freq = index.freq
    start = index[0]
    if end:
        extended = pd.date_range(
            start,
            end=end,
            freq=freq,
        )
    elif periods:
        extended = pd.date_range(
            start,
            periods=periods + len(index),
            freq=freq,
        )
    return extended