On Tuesday 31 May 2016 14:27, Sayth Renshaw wrote:
>
> Hi
>
> What is the best way to inplace alter a list going into a postgres database
Is it relevant where it is going?
What you do with the list after you alter it is irrelevant -- perhaps you will
insert it into an Oracle database, or a place it in a dict, or print it. The
only reason it might be relevant is if Postgres can do the work for you, so you
don't need to split it in Python. And that's probably a question for a Postgres
group, not a Python group.
> using split but being sure that the order of items remains correct.
To modify a list *in place* is tricky. You can use slicing, which is easy, but
because the size of the list changes you need to work backwards from the end.
I will use 'x' for fields that don't change, and suppose you wish to split
fields 9, 10, 11 and 12. (Remember that Python counts starting from 0, not 1.)
L = ['x', 'x', 'x', 'x', 'x', 'x', 'x', 'x', 'x',
'11-3-1-4 $72390.00',
'2-0-0-2 $8970.00',
'3-2-0-0 $30085.00',
'3-1-0-0 $15450.00',
'x', 'x', 'x'
]
for index in (12, 11, 10, 9): # must process them in *reverse* order
item = L[index]
values = item.replace('-', ' ').split()
L[index:index+1] = values # slice assignment
Perhaps a better way is to build a new list:
L = ['x', 'x', 'x', 'x', 'x', 'x', 'x', 'x', 'x', '11-3-1-4 $72390.00',
'2-0-0-2 $8970.00', '3-2-0-0 $30085.00', '3-1-0-0 $15450.00',
'x', 'x', 'x']
new = []
for i, item in enumerate(L):
if i in (9, 10, 11, 12):
values = item.replace('-', ' ').split()
new.extend(values)
else:
new.append(values)
You can then replace L with new *in-place* with a slice:
L[:] = new
or just use new instead.
--
Steve
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