Python How to print list of list

Question

I want to print list of list in python 3.x with below code, but it is giving an error.

lol=[[1,2],[3,4],[5,6],['five','six']]
for elem in lol:
      print (":".join(elem))
# this is the error I am getting-> TypeError: sequence item 0: expected str instance, int found

I am expecting this output:

1:2
3:4
5:6
five:six

I could achieve the same output using below perl code (this is just for reference):

for (my $i=0;$i<scalar(@{$lol});$i++)
{
    print join(":",@{$lol->[$i]})."\n";
}

How do I do it in python 3.x?

score 7 · Answer 1 · answered Jun 22 '13 at 14:57

7

I'd go for:

for items in your_list:
    print (*items, sep=':')

This takes advantage of print as a function and doesn't require joins or explicit string conversion.

answered Jun 22 '13 at 14:57

Jon Clements

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@Ashwini yeah... sometimes quite painful having to use `print` as a statement :-( – Jon Clements Jun 22 '13 at 15:07
if nothing else should be done with result this is the best solution – oleg Jun 22 '13 at 19:08
@Jon and oleg: Well, it seems to *me* tricky. I was thinking about `print` being just a replacement for the later processing of items. I do not know. Possibly... *"Explicit is better than implicit."* – pepr Jun 22 '13 at 20:51

oleg · Accepted Answer · 2013-06-22T14:51:09.300

3

One can't join int's only strings. You can Explicitly cast to str all your data try something like this

for elem in lol:
    print (":".join(map(str, elem)))

or with generator

for elem in lol:
    print (":".join(str(i) for i in elem))

or You can use format instead of casting to string (this allows You to use complex formatting)

for elem in lol:
    print (":".join("'{}'".format(i) for i in elem))

edited Jun 22 '13 at 14:51

answered Jun 22 '13 at 14:45

oleg

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That's a comprehension, not a generator. – Mel Nicholson Jun 22 '13 at 14:50
`str.join` converts the genexp into a list first before actually joining them. http://stackoverflow.com/a/9061024/846892 – Ashwini Chaudhary Jun 22 '13 at 14:50
this is internal implementation of join as I understand. `":".join(str(i) for i in elem)` itself is generator – oleg Jun 22 '13 at 14:52
@oleg: More precisely, the `str(i) for i in elem` is a generator expression. It is used as an argument of `.join()`, this way, the extra parentheses need not to be used. Anyway, the `g = (str(i) for i in elem)` defines a generator named `g`, and then one can write `print(":".join(g))` just after the `g = ...` (the same indentation). The `str.join()` method accepts any iterable that returns strings. Because of that, it can consume also a generator or a generator expression. – pepr Jun 22 '13 at 17:19

score 1 · Answer 3 · answered Jun 22 '13 at 14:44

Use a list comprehension and str.join:

Convert the integers to string(using str()) before joining them

>>> lis = [[1,2],[3,4],[5,6],['five','six']]
>>> print ("\n".join([ ":".join(map(str,x))   for x in lis]))
1:2
3:4
5:6
five:six

or:

>>> print ("\n".join([ ":".join([str(y) for y in x])   for x in lis]))
1:2
3:4
5:6
five:six

Python How to print list of list

3 Answers3

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