Python help using for loop to change x

Question

First, today is the first time I have used Python. I used Perl 15 years ago, so very rusty but eager to learn. I'm trying to convert the following lines into a for loop, using x to increment ONrelay (so ONrelay0, ONrelay1, ONrelay3, and so on):

cpi6x.setbit(board1, cpi6x.ONrelay0)
time.sleep(.300)
cpi6x.setbit(board1, cpi6x.ONrelay1)
time.sleep(.300)
cpi6x.setbit(board1, cpi6x.ONrelay2)
time.sleep(.300)
cpi6x.setbit(board1, cpi6x.ONrelay3)
time.sleep(.300)
cpi6x.setbit(board1, cpi6x.ONrelay4)

I have tried the following, but not surprisingly it doesn't work.

for x in range(0, 5):
    cpi6x.setbit(board1, cpi6x.ONrelay%d) % (x)
    time.sleep(.300)

Any help would be much appreciated!

score 5 · Accepted Answer · answered Jan 04 '16 at 16:42

5

That won't work as ONrelay is not a string, but instance attributes, use getattr instead:

for i in range(5):
    obj = getattr(cpi6x, 'ONrelay{}'.format(i))
    cpi6x.setbit(board1, obj)
    time.sleep(.300)

answered Jan 04 '16 at 16:42

Iron Fist

10,739
2
18
34

1

or, with `%`-style formatting: `getattr(cpi6x, 'ONrelay%d' % i)` – GingerPlusPlus Jan 04 '16 at 16:52
@GingerPlusPlus .. correct...That will work too – Iron Fist Jan 04 '16 at 17:16

score 0 · Answer 2 · answered Jan 04 '16 at 17:14

It would be easier and more Pythonic to put the relays in an array:

relays = [cpi6x.ONrelay0,
          cpi6x.ONrelay1,
          cpi6x.ONrelay2,
          cpi6x.ONrelay3,
          cpi6x.ONrelay4]

for relay in relays:
    cpi6x.setbit(board1, relay)
    time.sleep(.300)

You could also access the individual relays as relays[x] instead of separate variable names.

Python help using for loop to change x

2 Answers2