[Tutor] pointers or references to variables or sub-sets of variables query.

[David L Neil]

On 8/07/19 2:48 AM, Alan Gauld via Tutor wrote:
> On 07/07/2019 09:19, David L Neil wrote:
>> First-off, it has to be said that "100's of elements" suggests using an
>> RDBMS - particularly if 'age' (eg 23 and 99) is not the only likely
>> selection mechanism.
> 
> Multiple selection mechanisms might suggest an RDBMS but hundreds of
> items is chickenfeed and an RDBMS would be overkill for such small
> numbers, if volume was the only criteria. Millions of items would
> certainly warrant such an approach but nowadays holding 10's of
> thousands of items in memory is entirely reasonable.


Assuming plentiful RAM: agreed.
(However, some of us grew-up at a time when RAM was expensive and even 
in our relaxed state, such 'costs' still impinge on our consciousness - 
also, in another thread (here?Python list) we had someone frustrated 
about using an MS-Vista 'powered' machine and limited to 32-bits. We 
don't know the OP's circumstances. That said, loading an RDBMS, if (s)he 
doesn't already have one, is...)

As you point-out, with memory more-commonly available, I've obtained 
significant speed improvements by moving relatively small, and 
particularly temporary, DB tables into MySQL's MEMORY storage (and with 
almost zero code-change/risk)!
(so, it IS possible to teach old dogs new tricks)


The key justification for moving to RDBMS would be "not the only 
selection mechanism". Whereas a Python dictionary (hash) offers speedy 
access to data based upon a single index, it is hard to beat the bug- 
and time-saving facility of a DB managing multiple indices/indexes.
(appreciating that I have no difficulty moving from (Python) procedural 
programming to (SQL) declarative, but many of our colleagues hate such, 
and with a passion)


So, using the OP's data-example, and assuming the 'columns' to be 
perhaps employment_date, name, and age; respectively:

['2019-01-19','Fred Flintstone',23],
['2019-02-01','Scooby doo', 99]

- which Python (and pythonic - per OP's theme) structures and methods 
offer a relatively bug-unlikely solution to holding *multiple* indices 
into a base list (or other collection)?
(alternately, maybe we should wait for the OP, and allow opportunity to 
complete the homework first?)

(NB this may be veering OT, if the OP requires only the single access 
method, such as that illustrated earlier)
-- 
Regards =dn