Python Convert String to List of Lists of Strings

Question

I have the current string:

output = "S.##......\n#.##..###.\n#.###.###.\n#.....###.\n###.#####S"

I want to convert it to the following list:

coordinates = [['S', '.', '#', '#', '.', '.', '.', '.', '.', '.'],
               ['#', '.', '#', '#', '.', '.', '#', '#', '#', '.'],
               ['#', '.', '#', '#', '#', '.', '#', '#', '#', '.'],
               ['#', '.', '.', '.', '.', '.', '#', '#', '#', '.'],
               ['#', '#', '#', '.', '#', '#', '#', '#', '#', 'S']]

Basically every time I get a "\n" character, I want the sequence before it to be split like above and put in a separate list item. I tried the following:

    coordinates = []
    temp = []
    for item in output:
        if item != "\n":
            temp += item
        else:
            coordinates += temp

but it doesn't work, neither it works with

.append()

Martijn Pieters · Accepted Answer · 2014-10-23 16:25:55Z

4

Split on newlines with str.splitlines() (to avoid producing an empty last line), then call list() on each resulting string. You can do this all in one expression with a list comprehension:

[list(line) for line in output.splitlines()]

Calling list() on a string creates a list object of the individual characters:

>>> list('foo')
['f', 'o', 'o']

Demo:

>>> from pprint import pprint
>>> output = "S.##......\n#.##..###.\n#.###.###.\n#.....###.\n###.#####S"    
>>> [list(line) for line in output.splitlines()]
[['S', '.', '#', '#', '.', '.', '.', '.', '.', '.'], ['#', '.', '#', '#', '.', '.', '#', '#', '#', '.'], ['#', '.', '#', '#', '#', '.', '#', '#', '#', '.'], ['#', '.', '.', '.', '.', '.', '#', '#', '#', '.'], ['#', '#', '#', '.', '#', '#', '#', '#', '#', 'S']]
>>> pprint(_)
[['S', '.', '#', '#', '.', '.', '.', '.', '.', '.'],
 ['#', '.', '#', '#', '.', '.', '#', '#', '#', '.'],
 ['#', '.', '#', '#', '#', '.', '#', '#', '#', '.'],
 ['#', '.', '.', '.', '.', '.', '#', '#', '#', '.'],
 ['#', '#', '#', '.', '#', '#', '#', '#', '#', 'S']]

Your attempt fails because you never reset temp; you'd need to create a new empty list each time you reach \n, and use coordinates.append() instead of += (which is the same as coordinates.extend():

coordinates = []
temp = []
for item in output:
    if item != "\n":
        temp += item
    else:
        coordinates.append(temp)
        temp = []
if temp:
    coordinates.append(temp)

You need the last two lines to not miss the last line after the last '\n' character.

edited Oct 23, 2014 at 16:25

answered Oct 23, 2014 at 16:19

Martijn Pieters

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6 Comments

linuxfan Over a year ago

Hi Martijn: can you please explain how _ is set?

Martijn Pieters Over a year ago

@linuxfan: the Python terminal sets _ to the last echoed result. So any expression you execute that doesn't return None has the result printed to the terminal, and _ is set.

David Sanders Over a year ago

I prefer this answer over .split('\n') since I'm presuming it's line-ending style agnostic (Windows vs. Unix).

Martijn Pieters Over a year ago

@DavidSanders: it is.

Martijn Pieters Over a year ago

@DavidSanders: I used it here because 'foo\nbar\n'.split('\n') produces a list with three elements, but 'foo\nbar\n'.splitlines() produces a list with only two elements.

|

Alex Riley · Accepted Answer · 2014-10-23 19:36:14Z

You could use a list comprehension to generate each list of characters between the \n delimeter:

>>> [list(x) for x in output.split('\n')]
[['S', '.', '#', '#', '.', '.', '.', '.', '.', '.'],
 ['#', '.', '#', '#', '.', '.', '#', '#', '#', '.'],
 ['#', '.', '#', '#', '#', '.', '#', '#', '#', '.'],
 ['#', '.', '.', '.', '.', '.', '#', '#', '#', '.'],
 ['#', '#', '#', '.', '#', '#', '#', '#', '#', 'S']]

Passing a string x to list returns a list of the characters in x. output.split('\n') is one way to break your string output into a list of strings which were separated by the newline character \n.

Edit: The answer written by @MartijnPieters highlighted an important point about splitting stings on \n (which I admit I wasn't aware of).

If your string has a trailing \n it may be preferable to use output.splitlines() to split the string. Here, using split('\n') would return an empty string after the final \n, whereas splitlines() avoids this by default.

Cory Kramer · Accepted Answer · 2014-10-23 16:19:13Z

1

You can split on newlines '\n' then convert to lists.

output = "S.##......\n#.##..###.\n#.###.###.\n#.....###.\n###.#####S"
coordinates = [list(s) for s in output.split('\n')]

>>> coordinates
[['S', '.', '#', '#', '.', '.', '.', '.', '.', '.'],
 ['#', '.', '#', '#', '.', '.', '#', '#', '#', '.'],
 ['#', '.', '#', '#', '#', '.', '#', '#', '#', '.'],
 ['#', '.', '.', '.', '.', '.', '#', '#', '#', '.'],
 ['#', '#', '#', '.', '#', '#', '#', '#', '#', 'S']]

answered Oct 23, 2014 at 16:19

Cory Kramer

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Comments

dpgaspar · Accepted Answer · 2014-10-24 08:26:43Z

1

This should work:

output = "S.##......\n#.##..###.\n#.###.###.\n#.....###.\n###.#####S"
items = output.split('\n')
final_list = []
for item in items:
    line_list = [c for c in item]
    final_list.append(line_list)


print final_list

edited Oct 24, 2014 at 8:26

answered Oct 23, 2014 at 16:24

dpgaspar

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