如何遍历列表列表并将每个列表的项目打印为逗号分隔的字符串

Question

If I have a list of lists:

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

How do I iterate over these lists and print them to get the following output?

1, 2, 3
4, 5, 6
7, 8, 9

Answer 1

Try this:

for l in x:
    print ', '.join(map(str, l))

Output:

1, 2, 3
4, 5, 6
7, 8, 9

Answer 2

You pretty much have it:

# python
x = [['1','2','3'],['4','5','6'],['7','8','9']]

for i in x:
  print i[0]
1
4
7

for i in x:
  print i
['1', '2', '3']
['4', '5', '6']
['7', '8', '9']

for i in x[0]:
  print i
1
2
3

Answer 3

You can use itertools.chain :

from itertools import chain

for i in chain.from_iterable(x):
    print i

Answer 4

If you're talking about processing each element in the arrays one-by-one (I'm assuming here that the printing is just an example and your your actual desired processing is more complicated), the simplest way is to not do that. You obviously have your data structured in that way for a reason, in which case your code should mirror it.

You save very little by doing that with a single for statement so I would use:

for xlist in x:
    for n in xlist:
        do something with n

Believe it or not, having your code mirror your data actually improves code readability.

As an example, to get your exact output as specified in the edit:

#!/usr/bin/python

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

for xlist in x:
    s = ""
    for n in xlist:
        s = "%s, %c"%(s,n)
    print s[2:]

Answer 5

Just for the concept, the actual traversal is very simple:

for i in x: #a list
    for j in i: #elements of the list
        print j

This will print 1 2 3 4 5 6 7 8 9, every number in a newline

You can change the pattern as you would want.

Answer 6

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

[k for y in x for k in y]

Output:

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