Multiple equates

[Iain King]

On Nov 17, 7:41 pm, Tim Chase <python.l... at tim.thechases.com> wrote:
> > It doesn't matter as none of this is valid Python. In Python you have to
> > write
>
> > array[x1] = False
> > array[x2] = False
>
> Uh...not so much...
>
>   >>> a = [1,2,3,4,5]
>   >>> x1, x2 = 1, 3
>   >>> a[x1] = a[x2] = False
>   >>> a
>   [1, False, 3, False, 5]
>
> Works for me.
>
> To the OP, I think rather than cluttering my code, I'd just
> create a loop
>
>    for i in [x1,x2,x3,x4,...x1024]:
>      a[i] = False
>
>  From Diez's disassembly of it (as an aside, nifty little intro
> to dis.dis()...thanks, Diez!), it looks like it boils down to "is
> DUP_TOP faster than LOAD_CONST" because the rest of the
> operations.  At this point, it's pretty nitty-gritty.
>
> Unless the code is in an inner loop somewhere, the simple loop
> should be more than fast enough.  Without knowing the source of
> the [x1,...] index variables, it's hard to tell if there's a more
> optimal way to do this.
>
> -tkc

The loop is much nicer, especially as your array gets longer.  The
generic:

for i in xrange(array):
    array[i] = False

will set the entire array.

Regarding your original question:

array[x1] = array[x2] = False

array[x1] = False
array[x2] = False

These two blocks are functionally the same when you are setting to
True or False (or any immutable), but are not if  setting to
immutables, which could give you some real head-scratching bugs if you
were unaware of the difference - the first version assigns the same
object to both names:

>>> array[x1] = array[x2] = []
>>> array[x1].append("Hi")
>>> array[x2]
['Hi']


Iain