Python: convert str to integer

Question

I'm new at Python and I have an assginment which is read a file and convert it to matrix. My file is:

n 5
0 -- 3
0 -- 4
1 -- 2
1 -- 3
2 -- 4
3 -- 3

First of all,I have to make a "5X5" matrix. I read 5 like this:

f = open("graph.txt")
    mylist = f.readlines()
    a = mylist[0][2]

When say print a it prints 5. In order to make a matrix I need to convert this string to integer. However, when I used int(a) function, it remained a str. How can I change it to integer permanently?

You probably also want to look into the `.split()` method to split strings into chunks based on whitespace. That looks like a tool you're going to need. — Tim Pietzcker, Mar 04 '13 at 09:06
What does the resultant matrix look like? Could you please post it? — Snakes and Coffee, Mar 04 '13 at 09:08
***Closely related***: [How to read numbers from file in Python?](http://stackoverflow.com/q/6583573/78845) — johnsyweb, Mar 04 '13 at 09:09
When I use **.split()** for other lines, besides the first one, it splits last number (for example 3) with "3\n". How can I select just one item with this method? @TimPietzcker — jdyg, Mar 04 '13 at 09:12

score 3 · Answer 1 · answered Mar 04 '13 at 09:00

3

int creates a new value but does not change the original one. So, to actually change the value, you must do something like

list[0][2] = int(list[0][2])

answered Mar 04 '13 at 09:00

Fabien

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score 0 · Answer 2 · answered Mar 04 '13 at 09:03

0

use the int() constructor to assign to a:

a = int(list[0][2])

Note that this will raise an exception if the string cannot be converted to int.

answered Mar 04 '13 at 09:03

Ber

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Python: convert str to integer

2 Answers2