Print a nested list line by line - Python

Question

A = [[1, 2, 3], [2, 3, 4], [4, 5, 6]]

I am trying my best to print A of the form:

1 2 3
2 3 4
4 5 6

That is in different lines, but I am unable to do so without all the elements in different lines. This is my code so far:

for r in A:
   for t in r:
       print(t,)
    print

This is my output:

1
2
3
2
3
4
4
5
6

It seems really simple, and I think a minor change would do it. Thanks!

Answer 1

Use a simple for loop and " ".join() mapping each int in the nested list to a str with map().

Example:

>>> ys = [[1, 2, 3], [4, 5, 6], [7, 8, 9, 10]]
>>> for xs in ys:
...     print(" ".join(map(str, xs)))
... 
1 2 3
4 5 6
7 8 9 10

The difference here is that we can support arbitrary lengths of inner lists.

---

The reason your example did not work as expected is because your inner loop is iterating over each element of the sub-list;

for r in A:  # r = [1, 2, 3]
    for t in r:  # t = 1 (on first iteration)
        print(t,)
    print

And print() by default prints new-line characters at the end unless you use: print(end="") I believe if you were using Python 2.x print t, would work. For example:

>>> ys = [[1, 2, 3], [4, 5, 6], [7, 8, 9, 10]]
>>> for xs in ys:
...     for x in xs:
...             print x,
...     print
... 
1 2 3
4 5 6
7 8 9 10

But print(x,) would not work as you intended it; Python 2.x or 3.x