<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def default_value(fieldname, datatype):
 """ Return the default value for a column. If the column name (e.g. *i-wf*) is defined to have an idiosyncratic value, that value is returned. Otherwise the default value for the column's datatype is returned. Args: fieldname: the column name (e.g. `i-wf`) datatype: the datatype of the column (e.g. `:integer`) Returns: The default value for the column. .. deprecated:: v0.7.0 """

    if fieldname in tsdb_coded_attributes:
        return str(tsdb_coded_attributes[fieldname])
    else:
        return _default_datatype_values.get(datatype, '')