Retrieve a class from the registry.

    :raises: marshmallow.exceptions.RegistryError if the class cannot be found
        or if there are multiple entries for the given class name.

def get_class(classname, all=False):
    """Retrieve a class from the registry.

    :raises: marshmallow.exceptions.RegistryError if the class cannot be found
        or if there are multiple entries for the given class name.
    """
    try:
        classes = _registry[classname]
    except KeyError:
        raise RegistryError('Class with name {!r} was not found. You may need '
            'to import the class.'.format(classname))
    if len(classes) > 1:
        if all:
            return _registry[classname]
        raise RegistryError('Multiple classes with name {!r} '
            'were found. Please use the full, '
            'module-qualified path.'.format(classname))
    else:
        return _registry[classname][0]