On 2016-12-31 00:48, Deborah Swanson wrote:
On 30/12/16 23:00, Deborah Swanson wrote:
> Oops, indentation was messed up when I copied it into the email.
> Should be this:
>
> if len(l1[st]) == 0:
> if len(l2[st]) > 0:
> l1[st] = l2[st]
> elif len(l2[st]) == 0:
> if len(l1[st]) > 0:
> l2[st] = l1[st]
That's even worse!
Anyway, ignoring all that, if what you are trying to do is
just do some
action based on a set of fixed comparisons that are known at
the top of
the function (and do not mutate depending on the path through the
function), then you can just cache the comparisons and then
compare the
resulting set of boolean results (note that my examples are
NOT based on
your use-case, it's just pseudo-code which happens to use
your expressions):
state = (len(l1[st]) == 0, len(l2[st]) > 0)
if state == (True, False):
pass
elif state == (False, True):
pass
... etc.
If the len() comparisons are tri-state (i.e., in some cases
you want to
know if the length is <, ==, or > 0, depending on one of the other
comparisons) then you can do something like:
def clamp(foo):
return min(max(-1, foo), 1)
state = (clamp(cmp(len(l1[st]), 0), cmp(len(l2[st]), 0))
if state == (0, -1):
pass
elif state == (1, -1):
pass
... etc.
I'm not sure this makes it much more readable though - but if
you make
the RHS of those comparisons a symbolic name you might be getting
somewhere -
ACTION1 = (0, -1)
ACTION2 = (1, -1)
if state == ACTION1:
pass
elif state == ACTION2:
pass
Hope that helps, E.
Thanks Erik, I really like your method of capturing the state and then
reusing it. I'm sure I can use it in other situations. In this case,
since I now have it down to:
if not len(l1[st]) and len(l2[st]):
l1[st] = l2[st]
elif not len(l2[st]) and len(l1[st]):
l2[st] = l1[st]
[snip]
An empty list is considered falsey and a non-empty list is considered truey:
>>> bool([])
False
>>> bool([0])
True
You don't care what the list's length is, only whether it's 0 or not, so:
if not l1[st] and l2[st]:
l1[st] = l2[st]
elif not l2[st] and l1[st]:
l2[st] = l1[st]
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