Working through a list of lists in Python

Question

I'm pretty new to Python and am trying to work through a list of lists.

Say I have:

myList = [[1,2,3,4],[10,11,12,13],[29,28,27,26]]

and a function called myFunction

I could write:

for x in myList:
   for y in x:
     myFunction(y)

However, that would just call myFunction on each individual item in all the sublists. How would I incorporate something that I could also call when I finish up all the items in each sublist (e.g. I would call 1, 2, 3 and 4, and then the loop would realize it is at the end of the sublist and I could call that sublist).

Thanks so much!

falsetru · Accepted Answer · 2013-08-27 15:10:02Z

5

Do what you want in outer loop:

>>> for x in myList:
...     for y in x:
...         print(y)
...     print(x) # <---
...
1
2
3
4
[1, 2, 3, 4]
10
11
12
13
[10, 11, 12, 13]
29
28
27
26
[29, 28, 27, 26]

answered Aug 27, 2013 at 15:10

falsetru

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2 Comments

John Over a year ago

Thanks! What if what I would want to do in the outer loop can only be done once the item in the inner loop has been completed? In this case, I would want to work on the items in the inner loop for each sublist, then call the sublist, then move on to the items in the next sublist.

falsetru Over a year ago

@John, In the above code, print(x) is only executed only after the inner loop has been completed.

Community · Accepted Answer · 2017-05-23 10:25:16Z

1

John, it is indented syntax of Python, while it is indented it is a block of code, i.e. all commands are in pack (in block):

for x in myList:
    # block of code started
    for y in x:
        # here is new block
        # some here will be called totally "all elements in all sublists" times
        # i.e. "number of elements in x" times 
        # per "number of sublist in myList" times
        # and here will be called the same number of times (it is block)
    # here you're out of "for y in x" loop now (you're in previous block)
    # some here will be called "myList" number of times 
    # and here
# here you are out of "for x in myList" loop

edited May 23, 2017 at 10:25

CommunityBot

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answered Aug 27, 2013 at 15:23

rook

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Comments

badc0re · Accepted Answer · 2013-08-27 15:11:44Z

0

Hope this is what you want:

def myFunction(y):
    print y

myList = [[1,2,3,4],[10,11,12,13],[29,28,27,26]]

for x in range(len(myList)):
   print "Sublist:",x, myList[x]
   for y in myList[x]:
     myFunction(y)

answered Aug 27, 2013 at 15:11

badc0re

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