dynamic if statement

[Mark Lawrence]

On 18/06/2013 15:56, Tim Chase wrote:
> On 2013-06-18 07:10, upperdecksu at gmail.com wrote:
>> I have a set of queries that are run against various
>> databases/tables.  The result is all the same in that I always get
>> back the same field names.
>>
>> I query fld1, fld2, fld3, qty, qty2 from table1
>> then I loop thru the results
>>    if fld1 = 'a' add qty to some_total1
> ...
>> I created a database pair that contains (table1,fld1 = 'a',add qty
>> to some_total1) (table2,fld2 = 'b',qty to some_total1)
>>                                      (table3,fld3 = 'c',qty2 to
>> some_total1)
>
> Given the data-structure you have, and that it's hard-coded (rather
> than able to take dynamic/dangerous user input) for the table-name,
> I'd do something like this (untested)
>
>    for tablename, compare_field, compare_value, source_field in (
>        ("table1", "fld1", "a", "qty"),
>        ("table2", "fld2", "b", "qty"),
>        ("table3", "fld3", "c", "qty2"),
>        ):
>      # using string-building rather than escaping because
>      # 1) we know the tablenames are hard-coded/safe from above, and
>      # 2) this sort of escaping often chokes query parsers
>      query = "SELECT fld1, fld2, fld3, qty, qty2 from %s" % tablename
>      cursor.execute(query)
>
>      name_index_map = dict(
>        (info[0], i)
>        for info, i in enumerate(cursor.description)

Looks like this should be :-
for i, info in enumerate(cursor.description)

>        )
>      for row in cursor.fetchall():
>        db_value = row[name_index_map[compare_field]]
>        if db_value == compare_value:
>          addend = row[name_index_map[source_field]]
>          some_total_1 += addend
>
> -tkc
>

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Mark Lawrence