def update_postcode(postcode_value):
    """Update postcodes using mapping dictionary.
    
       Takes postcode value, updates using postcode_mapping
       dictionary and returns updated value.
    """
    postcode_mapping = {'78621' : '78681', '787664' : '78664', '78728-1275' : '78728'}

    if postcode_value not in postcode_mapping.keys():
        return postcode_value
    else:
        print(postcode_value, "cleaned to -->", postcode_mapping[postcode_value])
        return(postcode_mapping[postcode_value])