Reading multiple numbers from a text file

Question

I am new to programming in python and need help doing this.

I have a text file with several numbers like this:

12 35 21
123 12 15
12 18 89

I need to be able to read the individual numbers of each line to be able to use them in mathematical formulas.

Solution 1

In python, you read a line from a file as a string. You can then work with the string to get the data you need:

with open("datafile") as f:
    for line in f:  #Line is a string
        #split the string on whitespace, return a list of numbers 
        # (as strings)
        numbers_str = line.split()
        #convert numbers to floats
        numbers_float = [float(x) for x in numbers_str]  #map(float,numbers_str) works too

I've done it all in a bunch of steps, but you'll often see people combine them:

with open('datafile') as f:
    for line in f:
        numbers_float = map(float, line.split())
        #work with numbers_float here

---

Finally, using them in a mathematical formula is easy too. First, create a function:

def function(x,y,z):
    return x+y+z

Now iterate through your file calling the function:

with open('datafile') as f:
    for line in f:
        numbers_float = map(float, line.split())
        print function(numbers_float[0],numbers_float[1],numbers_float[2])
        #shorthand:  print function(*numbers_float)

Solution 2

Another way to do it is by using numpy's function called loadtxt.

import numpy as np

data = np.loadtxt("datafile")
first_row = data[:,0]
second_row = data[:,1]