@Stefan59: Oh I see, does this mean that anything in a string after an underscore "_" is recognized as a suffix function? So "suffix" is a python tool? And is "some_name" also a python function as it doesn't get defined anywhere? I guess that it is a wildcard?

@3pointedit: Nope, i'm not great at explaining things so I hope you can understand. The suffix is a variable the script defines, it can be anything. In the tutorial suffix is computered to be either R_ or L_ as thats what we want to move, but really it can be any name or length. len(suffix) command just mean grab the length of suffix, adding suflen = len(suffix) defines suflen for the first time and gives it the value of the length of suffix, tutorial it is always 2 because R_ and L_ have the length of 2. You may need to do some python tutorials before try to understand python in blender, it will help. Steve

@3pointedit: some_name is defined, it's the name of the first parameter of the rename function.

Whatever you pass as first parameter, it'll get the name some_name. For example, if you would call rename("steve", "L_"), it would act as if you had said some_name="steve" and suffix="L_".

@Stefan59: Thank you for your patience :-) I think that I will have to rewatch some more times. How does the script calculate that the suffix (which is only a variable with no fixed length) is 2 characters long? Does it read the underscore or are you defining the suffix in ob.name?

@3pointedit: There is less magic involved than that, the underscore is nothing special. This type of programming is called "imperative programming", which means that you tell the computer "do this, then do this, then do this". This means that len(suffix) is executed when the computer runs that bit of code. It doesn't matter that suffix can have different lengths at different times. The result of len(suffix) now is the length of suffix now. Try toying around with it in the interactive Python console.

@3pointedit: (5 minutes into tutorial) the function is defined def rename(some_name, suffix): and gets it value when called ob.name = rename(name, '_R')

so name is passed to some_name and '_R' is passed to suffix

@Stefan59: Thank you, I guess I am getting lost on the order of operations/definitions?

@vinc3r: You're right, a, b = c, d is the same as a = c and b = d.

The added benefit of the former is that it also works when (c, d) is returned from a function, so then you can do a, b = function_returning_c_and_d().

So I check list, in python doc, then change , as same as you did. for name, ob in bpy.data.objects.items():
ob.name = 'test_' + ob.name

it worked but the 'name' should be ob.name, is not it? actually even though I simply use name = 'test_' + name, all cube change name .

@sybren: thanks to take your time. I will try again your discribed code.

@sybren: Thanks I could understand better. so to chane obj.name in same loop need to use items()?

<code>for name, obj in bpy.data.objects.items(): if obj.location.x < 0: obj.name = 'Left_' + obj.name else: obj.name = 'Right_' +obj.name</code>

@fun2tax: My point is that you do not want to use one loop. Loop 1: given the object, figure out its new name. Loop 2: given the new names, assign them to the objects. Combining those in a single loop is not possible, as you should not modify the collection you're looping over.

@sybren: Thanks, one thing I still can not understand is, why I can change key values when I use "items()"? <quote>for ob_name, ob in bpy.data.objects.items(): ob.name = "aaa_" + ob.name</quote>

this code seems work for me. but it not recommended?

or I can use values(), and keys() in spite of items()

 for ob in bpy.data.objects.values():
    ob.name = "aaa_" + ob.name   

for name in bpy.data.objects.keys():
    new_name = "aaa_" + name
    bpy.data.objects[name].name = new_name

but

 for obj in bpy.data.objects:
    obj.name = "aaa_" + obj.name

directly change bpy.data.objects collection keys , in this loop, then it can not work?

Have blender 2.79 current build change about it? because, now it seems work , even though I use

for obj in bpy.data.objects:
obj.name = "aaa_" + obj.name

when I test same thing in 2.79 rc2, it actually added many "aaa_" about same objects . but I may prefer your recommend way, which make new dictionary for new name, then use two loop without change collection in one loop. thanks.

@fun2tax: Doing something the correct way is always preferrable to "it seems to work in this particular version of Blender" ;-)

@sybren: I could understand why it may cause problem by your answer. I just need to make it as habit, dividing 2 loop. ;-)

@Pranavjit Virdi: In such cases having an intermediary name can help out. For example, first you rename Cube_L → Cube_L_becomes_R and Cube_R → Cube_R_becomes_L. Then rename them again, Cube_L_becomes_R → Cube_R and Cube_R_becomes_L → Cube_L. Then you're sure that you don't get any naming collissions.

@Sybren A. Stüvel: _L_becomes_R is way more characters than suflen 2 which is already predefined, so i made it _E and _W (for east and west) but now it changes them to _E and _W only and i have to run the script another time for the _E to change to _L(which is what it was in the first place). another thing, even if i change the other object to have a different name the flipping of location doesn't work.

@Pranavjit Virdi: alright the flipping does work now(i am often amazed at my stupidity, the objects i tested were spread along the y axis instead of the x axis.) the rest of the prob still stands.

@Pranavjit Virdi: k it works... here is the code if anyone wants to see it.

import bpy

suffix_translations = {
    '_R': '_E',
    '_L': '_W',
}
suflen = 2  # all suffixes should be this length.
for name, ob in bpy.data.objects.items():
    suffix = name[-suflen:]

    if suffix in suffix_translations:
        new_suffix = suffix_translations[suffix]
        ob.name = name[:-suflen] + new_suffix

        ob.location.x *= -1

suffix_translations_b = {
'_E': '_L',
'_W': '_R',
}

for name, ob in bpy.data.objects.items():
    suffix_b = name[-suflen:]
    if suffix_b in suffix_translations_b:
        new_suffix_b = suffix_translations_b[suffix_b]
        ob.name = name[:-suflen] + new_suffix_b

@Pranavjit Virdi: wow i just realized you addressed this issue in the video completely, i had paused the video before that point and didn't bother to see the whole thing through, hehe.