Pure Python coalesce alternative.

coalesce.py

class Unset:
    """
    This class represent an unset instance.
    """


unset = Unset()


def first_or_default(sequence, condition=unset, default=None):
    """
    Returns the first or default value that matches with a condition.
    """
    sequence = iter(sequence) if condition is unset else filter(condition, sequence)

    try:
        return next(sequence)

    except StopIteration:
        return default


def coalesce(*sequence, default=None):
    """
    Returns the first valid element in sequence.
    """
    return first_or_default(sequence, None, default=default)