MRAB wrote:
> On 2014-08-31 18:37, Dennis E. Evans wrote:
>>
>> Hi
>>
>> I have a function that reads some meta data from a database and builds a
>> default order by and where clause for a table.
>> Is the a way to build the strings with out using the intermediate
>> list?
>>
>> the end result needs to look like this,
>>
>> self.OrderBy = "tableAlias.ColumnOne, tableAlias.ColumnTwo, ..."
>>
>> self.WhereClause = "(tableAlias.ColumnOne = ?) and
>> (tableAlias.ColumnTwo = ?) and ..."
>>
> You could use a generator comprehension:
>
> self.PkOrderBy =
> CommaSpace.join(defaultColumn.format(Ali=self.alias,
> ColLabel=oneRow[KeyLabelPos]) for oneRow in rows)
>
> Does that make the code clearer? I don't think so. Or faster? Not
> enough to be noticeable.
>
> Incidentally, there's no need to treat the single-row case specially:
>
> >>> ' and '.join(['first', 'second', 'third'])
> 'first and second and third'
> >>> ' and '.join(['first', 'second'])
> 'first and second'
> >>> ' and '.join(['first'])
> 'first'
The same goes for the no-rows case:
>>> " and ".join([])
''
You might also introduce a helper function to reduce code redundancy:
def ReadPkColumns(self) :
rows = self.cursor.fetchall()
def build_clause(sep, template):
return sep.join(
template.format(Ali=self.alias, ColLabel=row[KeyLabelPos])
for row in rows)
self.PkOrderBy = build_clause(CommaSpace, defaultColumn)
self.PkWhereClause = build_clause(andConjunction,
defaultColumnParaMarker)
General observations: don't microoptimize (always col = [] instead of
col.clear()) and don't comment your code to death ;)
Also: CommaSpace instead of the literal ", " string? When you bind it to
another value like
CommaSpace = ";\t"
you will also have to change the name to SemicolonTabulator anyway.
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