python: unpacking a string to a list

Question

The answer to a question on multiple-value elements in a config file (which exactly fits my needs) suggests to "unpack the string from the config". I read the doc for unpacking arguments lists suggested in several places but I fail to understand how this relates to my problem.

I am sure this must be obvious: having a string str = "123,456", how can I transform it into the list [123,456] (the number of elements separated by a comma in the string may vary)

Thank you.

Thank you for the responses. I learned something with the map() function. Also "str" is indeed a bad name for a function, I usually use the thisString version (but Murphy's law dictates that I used "str" when posting worldwide :)) — WoJ, Jun 25 '12 at 19:56

pcalcao · Answer 1 · 2012-06-25T16:00:56.793

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[int(x) for x in str.split(",")]

You're basically applying the function int to each element produced by split of your string.

The result of simply str.split(',') would be ["123","456"].

As Daniel Roseman pointed out, you should be careful not to use variable or method names that inadvertently overshadow built in methods, like, for instance, str.

edited Jun 25 '12 at 16:00

answered Jun 25 '12 at 15:47

pcalcao

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score 4 · Accepted Answer · answered Jun 25 '12 at 15:47

4

Do you want a list of strings or a list of ints?

If you just want a list of strings, it's very simple:

my_list = my_string.split(',')

If you want to convert these to ints, you need:

my_list = map(int, my_string.split(','))

(Also, don't use str as a variable name as it shadows the built-in str() function.)

answered Jun 25 '12 at 15:47

Daniel Roseman

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Out of curiosity, is there any noticeable difference in terms of performance between using `map` or simply the syntax I presented? – pcalcao Jun 25 '12 at 16:02
Not really. To be honest, I usually use the list comprehension myself, but typed in `map` this time because it's quicker to type :-) – Daniel Roseman Jun 25 '12 at 16:03

score 0 · Answer 3 · edited Jul 13 '12 at 19:51

0

The easiest way would be to use split().

unpacked = str.split(',')

edited Jul 13 '12 at 19:51

betabandido

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answered Jun 25 '12 at 15:46

TaoJoannes

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score 0 · Answer 4 · answered May 19 '15 at 02:56

Although I agree with the other answers, you should also handle exceptions in the case of invalid string representation of a supposed number. Take, for example, the following snippet:

number_string = "123,456,x21"
delimiter = ","
number_list = []
for item in number_string.split(delimiter):
    try:
        my_num = int(item)
        number_list.append(item)
    except ValueError, e:
        # you can choose to just pass or handle the error like so
        print "Skipping %s: %s" % (item, e.message)

Just a thought. Good luck!

python: unpacking a string to a list

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