How can I convert list of list with strings to list of list with ints in python?

Question

I have tried multiple ways to convert this, but all were unsuccessful. For example, my list is.

testscores= [['John', '99', '87'], ['Tyler', '43', '64'], ['Billy', '74', '64']]

I want to convert only the numbers to intergers because I will eventually average the actual scores later on and leave the names in a string.

I want my result to look like

testscores = [['John', 99, 87], ['Tyler', 43, 64], ['Billy', 74, 64]]

I've tried numerous for loops to try and only int the numbers in these lists but none have worked at all. If any of you need some of my test code, I can add. Thanks.

No, not necessarily. I'm hoping to get the code to work no matter now many internal lists I have, in case there are additional students to add later on. — Jim Davis
– Jim Davis, Commented Apr 20, 2013 at 19:23
I mean, not the number of the lists, but their own length, is that always like [name, score1, score2]? — bereal
– bereal, Commented Apr 20, 2013 at 19:24
But yes, each internal list only has 3 elements inside of it. The number of internal lists can change however. — Jim Davis
– Jim Davis, Commented Apr 20, 2013 at 19:24

bereal · Accepted Answer · 2013-04-20 19:24:37Z

2

In case if all the nested lists have length 3 (i.e. 2 scores per student), that's as simple as:

result = [[name, int(s1), int(s2)] for name, s1, s2 in testscores]

answered Apr 20, 2013 at 19:24

bereal

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Lev Levitsky · Accepted Answer · 2013-04-20 19:25:04Z

2

In Python 2, for arbitrary length of sublists:

In [1]: testscores = [['John', '99', '87'], ['Tyler', '43', '64'],
   ...: ['Billy', '74', '64']]

In [2]: [[l[0]] + map(int, l[1:]) for l in testscores]
Out[2]: [['John', 99, 87], ['Tyler', 43, 64], ['Billy', 74, 64]]

In Python 3 (or 2):

In [2]: [[l[0]] + [int(x) for x in l[1:]] for l in testscores]
Out[2]: [['John', 99, 87], ['Tyler', 43, 64], ['Billy', 74, 64]]

answered Apr 20, 2013 at 19:25

Lev Levitsky

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SimonT · Accepted Answer · 2013-04-20 19:52:30Z

There have been a few solutions posted already, but here's my try at this, without relying on try and except.

newScores = []
for personData in testScores:
    newScores.append([])
    for score in personData:
        if score.isdigit(): # assuming all of the scores are ints, and non-negative
            score = int(score)
        elif score[:1] == '-' and score[1:].isdigit(): # using colons to prevent index errors, this checks for negative ints for good measure
            score = int(score)
    newScores[-1].append(score)
testscores = newScores

On a side note, I suggest that you consider using the Python dict structure, which allows you to do something like this:

testScores = {} # or = dict()
testScores["John"] = [99,87]

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