<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def get_var(var, default='""'):
    '''get var inside notebook'''
    ret = os.environ.get('NBCONVERT_' + var)
    if ret is None:
        return default
    return json.loads(ret)