from datetime import datetime, timedelta, tzinfo

# identity function
identity = lambda x: x


def human_datetime(time: datetime) -> str:
    return "{:%Y-%m-%d %H:%M:%S}".format(time)


def human_timedelta(delta: timedelta) -> str:
    if delta.days == 0:
        days = ""
    elif delta.days == 1:
        days = "1 day, "
    else:
        days = f"{delta.days} days, "

    hours = delta.seconds // 3600
    minutes = (delta.seconds - (hours * 3600)) // 60
    return days + f"{hours:0>2}:{minutes:0>2}"  # zero-pad to two digits


def group_by_key(data: list, key: str) -> dict:
    """Groups a list of dicts by the value of their `key` into a dict of lists of dicts."""
    keys = set([item[key] for item in data])
    # initiate a dict with `keys` as keys and [] as values
    groups = dict.fromkeys(keys, [])
    for k in keys:
        groups[k] = [item for item in data if item[key] == k]

    return groups