Python: replacing a variable in a looping list

Question

I'm trying to go through a list and print out the list using a secondary list of variables.

The problem is that the variables in the list are getting assigned and set, but are not getting printed out properly. This feels like something really simple but I've been stumped for a day or so on it. Any help would be appreciated!

side = ""
sideLong = ""
sideShort = ""
sideList = ["Right", "Left"]


jointRemapList =[
    ["Char_Hips", "Root_M"],
    ["Char_" + sideLong + "Finger1", "IndexFinger1_" + sideShort],
    ["Char_" + sideLong + "Finger2", "IndexFinger2_" + sideShort]
    ]

for side in sideList:
    sideLong = side
    sideShort = side[0]

    for jointPair in jointRemapList:

        print sideLong, sideShort, jointPair

Expected output would be:

Left L ['Char_Hips', 'Root_M']
Left L ['Char_LeftFinger1', 'IndexFinger1_L']
Left L ['Char_LeftFinger2', 'IndexFinger2_L']
Right R ['Char_Hips', 'Root_M']
Right R ['Char_RightFinger1', 'IndexFinger1_R']
Right R ['Char_RightFinger2', 'IndexFinger2_R']

Python doesn't keep pointers to variables this way. "foo" + bar is not the string "foo" with the suffix of "whatever bar is when we print it", bar is evaluated immediately and the string is "foo" + "whatever bar is right now." — Adam Smith
– Adam Smith, Commented Jun 14, 2017 at 17:22

Tony · Accepted Answer · 2017-06-14 17:20:22Z

3

I think the problem is happening because you are creating jointRemapList outside of your sideList loop. You want the list to be created dynamically by sideLong and sideShort, so you need to recreate it on each increment of your loop. Like the following:

side = ""
sideLong = ""
sideShort = ""
sideList = ["Right", "Left"]

for side in sideList:
    sideLong = side
    sideShort = side[0]

    jointRemapList =[
        ["Char_Hips", "Root_M"],
        ["Char_" + sideLong + "Finger1", "IndexFinger1_" + sideShort],
        ["Char_" + sideLong + "Finger2", "IndexFinger2_" + sideShort]
        ]

    for jointPair in jointRemapList:

        print sideLong, sideShort, jointPair

answered Jun 14, 2017 at 17:20

Tony

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1 Comment

Adam Smith Over a year ago

I agree this is the better solution, though it's going to be a bit slower than the str.format approach of Jared's.

Jared Goguen · Accepted Answer · 2017-06-14 17:41:46Z

3

So the issue is that you are creating the strings when jointRemapList is created, and updates to sideLong and sideShort are not going to be reflected in those strings because strings are immuatable. Try using string formatting instead.

from itertools import product

joint_remap_list = [
    ["Char_Hips", "Root_M"],
    ["Char_{side}Finger1", "IndexFinger1_{abbrev}"],
    ["Char_{side}Finger2", "IndexFinger2_{abbrev}"]
]

sides = ["Left", "Right"]

for side, pair in product(sides, joint_remap_list):
    abbrev = side[0]
    formatted = [s.format(side=side, abbrev=abbrev) for s in pair]
    print side, abbrev, formatted

edited Jun 14, 2017 at 17:41

answered Jun 14, 2017 at 17:22

Jared Goguen

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1 Comment

Adam Smith Over a year ago

consider defining the formatted list on a separate line.

fmtd_joint_pair = [s.format(long=sideLong, short=sideShort) for s in jointPair]; print sideLong, sideShort, fmtd_join_pair

feels nicer to me.

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