Iterating through list of list in Python

two nested for loops?

 for a in x:
     print "--------------"
     for b in a:
             print b

It would help if you gave an example of what you want to do with the lists

So wait, this is just a list-within-a-list?

The easiest way is probably just to use nested for loops:

>>> a = [[1, 3, 4], [2, 4, 4], [3, 4, 5]]
>>> a
[[1, 3, 4], [2, 4, 4], [3, 4, 5]]
>>> for list in a:
...     for number in list:
...         print number
...
1
3
4
2
4
4
3
4
5

Or is it something more complicated than that? Arbitrary nesting or something? Let us know if there’s something else as well.

Also, for performance reasons, you might want to look at using list comprehensions to do this:

http://docs.python.org/tutorial/datastructures.html#nested-list-comprehensions

It sounds like you need to use recursion. Make a function to iterate through a list, and if it hits an item that is also a list, call itself to iterate on the member. Here’s a link to something similar:

http://www.saltycrane.com/blog/2008/08/python-recursion-example-navigate-tree-data/

If you wonder to get all values in the same list you can use the following code:

text = [u'sam', [['Test', [['one', [], []]], [(u'file.txt', ['id', 1, 0])]], ['Test2', [], [(u'file2.txt', ['id', 1, 2])]]], []]

def get_values(lVals):
    res = []
    for val in lVals:
        if type(val) not in [list, set, tuple]:
            res.append(val)
        else:
            res.extend(get_values(val))
    return res

get_values(text)

x = [u'sam', [['Test', [['one', [], []]], [(u'file.txt', ['id', 1, 0])]], ['Test2', [], [(u'file2.txt', ['id', 1, 2])]]], []]
output = []

def lister(l):
    for item in l:
        if type(item) in [list, tuple, set]:
            lister(item)
        else:
            output.append(item)

lister(x)

if you don’t want recursion you could try:

x = [u'sam', [['Test', [['one', [], []]], [(u'file.txt', ['id', 1, 0])]], ['Test2', [], [(u'file2.txt', ['id', 1, 2])]]], []]
layer1=x
layer2=[]
while True:
    for i in layer1:
        if isinstance(i,list):
            for j in i:
                layer2.append(j)
        else:
            print i
    layer1[:]=layer2
    layer2=[]
    if len(layer1)==0:
        break

which gives:

sam
Test
Test2
(u'file.txt', ['id', 1, 0])
(u'file2.txt', ['id', 1, 2])
one

(note that it didn’t look into the tuples for lists because the tuples aren’t lists. You can add tuple to the “isinstance” method if you want to fix this)

This can also be achieved with itertools.chain.from_iterable which will flatten the consecutive iterables:

import itertools
for item in itertools.chain.from_iterable(iterables):
    # do something with item    

Create a method to recursively iterate through nested lists. If the current element is an instance of list, then call the same method again. If not, print the current element. Here’s an example:

data = [1,2,3,[4,[5,6,7,[8,9]]]]

def print_list(the_list):

    for each_item in the_list:
        if isinstance(each_item, list):
            print_list(each_item)
        else:
            print(each_item)

print_list(data)

# house list of lists
house = [["hallway", 11.25], ["kitchen", 18.0], ["living room", 20.0], 
         ["bedroom", 10.75], ["bathroom", 9.50]]
         
for key, y in house :
    print('The ' + key + ' is ' + str(y) + ' sqm ')

mylist12 = [1,2,[3,4],[5,6,7],8]

print(dir(mylist12)) # iterable

for i in mylist12:
if (isinstance(i,list)) :
for j in i:
print(j)
else :
print(i)