Get a filename from given name without dangerous or incompatible characters.

def getFilename(name):
    """Get a filename from given name without dangerous or incompatible characters."""
    # first replace all illegal chars
    name = re.sub(r"[^0-9a-zA-Z_\-\.]", "_", name)
    # then remove double dots and underscores
    while ".." in name:
        name = name.replace('..', '.')
    while "__" in name:
        name = name.replace('__', '_')
    # remove a leading dot or minus
    if name.startswith((".", "-")):
        name = name[1:]
    return name