Python loop through list starting at index

Question

I am looking for a more pythonic way to loop though a list starting an an index then return the values contained in sub-lists eg:

values = [[1,2], [2], [1,3,4]]
n=1
for i, item in enumerate(values[n:]):
    i += n
    if i < len(values):
        for sub_value in values[i]:
            print("index: "+str(i)+ " list: "+str(item)+ " sub value: "+str(sub_value))

The code works as intended but is pretty ugly, any ideas to simplify it?

@thefourtheye I am pulling out the i+nth item from the main list, otherwise i starts at zero and I get the wrong sub-values — Don Smythe
– Don Smythe, Commented Mar 21, 2015 at 3:21
oop though a list starting an an index then return the values contained in sub-lists This contradicts with your program — thefourtheye
– thefourtheye, Commented Mar 21, 2015 at 3:24
This code looks a bit... off... is this your desired output?: index: 1 list: [2] sub value: 2 index: 2 list: [1, 3, 4] sub value: 1 index: 2 list: [1, 3, 4] sub value: 3 index: 2 list: [1, 3, 4] sub value: 4 — Hybrid
– Hybrid, Commented Mar 21, 2015 at 3:24
@Hybrid, yes that's is the output I'm after - I just realised may be cleaner to return the sub-lists as they are ie [2] and then [1,3, 4] and then just iterate over them. — Don Smythe
– Don Smythe, Commented Mar 21, 2015 at 3:29

craighagerman · Accepted Answer · 2015-03-21 04:02:43Z

2

I'm not sure I completely understand what you are trying to achieve.If you want to print a flat list of the items from index 1 you could do this:

[item for sublist in values[1:] for item in sublist]

which produces:

[2, 1, 3, 4]

answered Mar 21, 2015 at 4:02

craighagerman

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Hybrid · Accepted Answer · 2015-03-21 04:19:21Z

0

I'm going to take a swing here and guess that you are trying to make a simple python function that loops through a list and prints out every element in the sublists. Here is the easiest way to do it:

def get_sublists(start=0):
    values = [[1,2], [2], [1,3,4]] 
    index = start 
    item = 0
    for value in values[index:]: 
        for sub_value in value: 
            print("Item: %s // Index: %s // List: %s // Sub Value: %s" % (item, index, values[index], sub_value)) 
            item += 1
        index += 1

get_sublists(1)

This will print out the following:

Item: 0 // Index: 1 // List: [2] // Sub Value: 2                                                                                                                                                                                                       
Item: 1 // Index: 2 // List: [1, 3, 4] // Sub Value: 1                                                                                                                                                                                                 
Item: 2 // Index: 2 // List: [1, 3, 4] // Sub Value: 3                                                                                                                                                                                                 
Item: 3 // Index: 2 // List: [1, 3, 4] // Sub Value: 4

I am not 100% sure about the question because it is a bit ambigous, so let me know if you have any further modifications.

edited Mar 21, 2015 at 4:19

answered Mar 21, 2015 at 4:00

Hybrid

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2 Comments

Don Smythe Over a year ago

your comments made me think a bit more about what I was trying to do and I came up with this: def getSubLists(start, values): for i, item in enumerate(values[start:]): for value in item: print(str(value)) values = [[1,2], [2], [1,3,4]] getSubLists(1, values) This way I can start my iteration at a specific location

Hybrid Over a year ago

Oh, I finally understand. In that case, you can use @craighagerman's solution since it uses List Comprehension, which is very efficient. If you want a more detailed output, you can use the function I provided above.

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