import re


def urlify(s):
    """
    Replacing spaces, and other URL-hostile characters
    like question marks, apostrophes, exclamation points, etc.

    Example:
    >>> s = 'iso met'
    iso_met
    >>> s = 'isomet?'
    'isomet'
    """
    # Remove all non-word characters (everything except numbers and letters)
    s = re.sub(r"[^\w\s]", "", s)

    # Replace all runs of whitespace with a single dash
    s = re.sub(r"\s+", "_", s)

    return s