Python - read numbers from text file and put into list

Question

So like the title says im starting to learn some python and im having trouble picking up on this technique. What I need to accomplish is to read in some numbers and store them in a list. The text file looks like the following:

0 0 3 50

50 100 4 20

Basically these are coordinates and directions to be used for python's turtle to make shapes. I got that part down the only problem is getting them in a correct format. So what I can not figure out is how to get those numbers from the file into [ [0, 0, 3, 50], [50, 100, 4, 20] ] A list, with each four coordinates being a list in that one big list.

Heres my attempt but it as I said I need some help - thank you.

polyShape=[]
infile = open(name,"r")
num = int(infile.readline(2))
while num != "":
    polyShape.append(num)
    num = int(infile.readline(2))
infile.close()

Answer 1

with open('data.txt') as f:
    polyShape = []
    for line in f:
        line = line.split() # to deal with blank 
        if line:            # lines (ie skip them)
            line = [int(i) for i in line]
            polyShape.append(line)

will give you

[[0, 0, 3, 50], [50, 100, 4, 20]]

This will work with a file that contains blank lines (or not).

Using the with construct will close the file for you automatically when you are done, or an exception is encountered.

Answer 2

Assuming there isn't actually a blank line in your input file:

with open(name, "r") as infile:
    polyShape = [map(int, line.split()) for line in infile]

Explanation: map(int, line.split()) splits each line and converts each part to an int. The [X for Y in Z] construct is a list comprehension that in turn maps the map over all lines of the file and returns its results in a list.

If you find this too complicated for now, then the map(int, line.split()) is the main take-home message.

Answer 3

with open('data.txt') as f:
    lis=[map(int,x.split()) for x in f if x.strip()]   # if x.strip() to skip blank lines

   #use list(map(int,x.split()))  in case of python 3.x

this is how map() works:

>>> map(int,'1 2 3 4'.split())
[1, 2, 3, 4]

Answer 4

One-liner:

[ [int(x) for x in line.split(' ')] for line in open(name,'r').readlines() if line.strip()]

but the readlines part is probably not a great idea.

I'm quite sure that [int(x) for x in ... ] is faster than using map as in other suggested solutions.

Edit

Thanks to Blender : no need for .readlines, which is cool, so we just have :

[ map(int, line.split()) for line in open(name,'r') if line.strip()]

I also used map(int, ) because it's actually faster, and also you can use just line.split() instead of line.split(' ').

Answer 5

Iterating over the file would be the easiest way:

poly_shape = []

with open(name, 'r') as handle:
    for line in handle:
        if not line.strip():
            continue  # This skips blank lines

        values = map(int, line.split())
        poly_shape.append(values)

Answer 6

I do not recommend using append for a big array. It's 50 time slower than creating a zero array and assigning values to it.

import numpy
fname = "D:\Test.txt";
num_lines = sum(1 for line in open(fname));
array = numpy.zeros((num_lines,4));
k = 0;
with open(fname, "r") as ins:
    for line in ins:
        a =[int(i) for i in line.split(' ')];;
         array[k,0:4] =a;
         k = k+1;
print(array)