Python: One more on lists

Coding
1

Hi, i´m pretty new to maya programming and i have a super noob question… (i´m sorry if it´s discussed in any other thread, i haven´t found it)

If i have a list with “x” number of elements, all of them in the same hierarchy, how could i do an action from the last to the first item? For example, to have a list of 6 elements, and want to make an aim constraint from the 6 to 5, 5 to 4… etc. (and without depending on any string).

Thanks!

2

Use negative list indices to iterate from the end of a list to its second item, use the current index-1 as the object to constrain.

I didn’t test this but it should run.

for i in range(1, len(items)):
    target = items[-i]
    to_constrain = items[-i-1]
    cmds.aimConstraint(target, to_constrain)
3

maybe something like this:


items = ['a', 'b', 'c', 'd', 'e', 'f']

for source, target in zip(reversed(items[:-1]),reversed(items[1:])):
	print "bind {0} to {1}".format(source,target)

prints:
bind e to f
bind d to e
bind c to d
bind b to c
bind a to b
4

maybe something like this:


items = ['a', 'b', 'c', 'd', 'e', 'f']

for source, target in zip(reversed(items[:-1]),reversed(items[1:])):
	print "bind {0} to {1}".format(source,target)

prints:
bind e to f
bind d to e
bind c to d
bind b to c
bind a to b

… or even


items = ['a', 'b', 'c', 'd', 'e', 'f']

target = items[-1]
for source in items[-2::-1]:
	print "bind {0} to {1}".format(source,target)
	target = source
5

Oh sure, i was forgetting totally the negative index.
Thanks a lot! ^^

6

Weird, must have been some server oddities. I didn’t see uiron’s post before posting. You have a few different options, at least.

7

Python has awesome tools for dealing with lists and orders. The slice syntax (my_list[1:3]) has and option argument for interval, which you can use for all sorts of cool tricks:


numbers = list(range(11))
print numbers        # the whole list

# first two arguments are 'start' and 'end' range
print numbers[1:3]   # items at position 2 and position 3

# use negative numbers to get position bac from the end
print numbers[1:-1]  # from the second to the second-to-last items

# 3rd item controls the interval
print numbers[0::2]  # start at zero, take every other
print numbers[1::2]  # start at one, take every other
# use negative interval to go backwards
print numbers[-1::-3]  # count back from 10 by threes

# use 'zip' to pair up items
evens =  numbers[0::2]
odds =  numbers[1::2]
print zip(evens, odds)  # a list of even, odd paies
print zip(evens, odds)[::-1] # even odd pairs reversed