Call a list variable from a for loop in Python

Question

If I have pre-set list variables that are the same name except for they end in a different number, how can I create variables in a for loop that will call those lists?

My issue is that the variable I create in the for loop is staying as a string. I need it to recognize that it's simply a name of a variable.

Example:

list1 = [2, 4, 3, 7]
list2 = [4, 5, 6]
list3 = [9, 5, 7, 8, 3, 2, 1]
list4 = [4, 1]

for i in range(1,5):
    print ("list%d" % (i))

This results in printing the strings:

list1

list2

list3

list4

I want it to print out the actual lists.

Thanks for any help!

Any time you think you need dynamic variable names like this, you're doing it wrong. Use an array or dictionary. — Barmar, May 06 '16 at 01:41
Use a nested array that you can index using your `i` variable — OneCricketeer, May 06 '16 at 01:42
Duplicate of http://stackoverflow.com/questions/8028708/dynamically-set-local-variable-in-python ? — sebacastroh, May 06 '16 at 01:43

score 6 · Accepted Answer · answered May 06 '16 at 01:49

You can achieve below as by using 'eval'.

list1 = [2, 4, 3, 7]
list2 = [4, 5, 6]
list3 = [9, 5, 7, 8, 3, 2, 1]
list4 = [4, 1]

for i in range(1,5):
    print (eval('list%d'% (i)))

But as mentioned in comments, this is not recommended. You should rewrite by dict or list of list i.e.

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

for i in range(len(my_list)):
    print (my_list[i])

Note that i change the name of variable list to my_list because the word list is a reserved word.

score 3 · Answer 2 · answered May 06 '16 at 01:47

You are printing a string literal (i.e. plain text) not the actual variable of each list. One thing you can do is put those lists in a class or a dictionary.

Assuming it's a class:

class cls:
    list1 = [2, 4, 3, 7]
    list2 = [4, 5, 6]
    list3 = [9, 5, 7, 8, 3, 2, 1]
    list4 = [4, 1]


for i in range(1, 5):
    print getattr(cls, 'list{}'.format(i))

Assuming it's a dictionary:

lists = {
    'list1': [2, 4, 3, 7],
    'list2': [4, 5, 6],
    'list3': [9, 5, 7, 8, 3, 2, 1],
    'list4': [4, 1],
}

for k, v in lists.items():
    print '{0}={1}'.format(k, v)

score 2 · Answer 3 · answered May 06 '16 at 01:49

2

As suggested in the comments you should consider some other data structue to use here.

If you still want this to work. You may try as below

for i in range(1,5):
    print (eval("list"+str(i)))

answered May 06 '16 at 01:49

Ashish

266
2
9

score 2 · Answer 4 · answered May 06 '16 at 02:09

the issue with your code that you print a string not the list variable

to loop through a list variable

list1 = [2, 4, 3, 7]
list2 = [4, 5, 6]
list3 = [9, 5, 7, 8, 3, 2, 1]
list4 = [4, 1]

for i in list1:
    print (i)

or you can put all the lists in a list and loop through it

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

for e in new_list:
    print(e)

you can also put all of them in a dictionary structure {key,value}

dic_of_lists={"list1":[2, 4, 3, 7],"list2":[4, 5, 6]
          ,"list3":[9, 5, 7, 8, 3, 2, 1],"list4":[4, 1]}

#to loop through the dictionary
for key,value in dic_of_lists.items():
    print(key+" : ")
    print(value)

Call a list variable from a for loop in Python

4 Answers4

to loop through a list variable

or you can put all the lists in a list and loop through it

you can also put all of them in a dictionary structure {key,value}