TypeError: list indices must be integers, not tuple

Question

My code:`

#!/usr/bin/python

with open("a.dat", "r") as ins:
    array = []
    for line in ins:
        l=line.strip()
        array.append(l)

a1 = array[:,1]
print a1

I want to read a.dat as array then take the first column.What is wrong?

Answer 1

For loading numerical data, it's often useful to use numpy instead of just Python.

import numpy as np
arr = np.loadtxt('a.dat')
print arr[:,0]

numpy is a Python library that's very well suited to loading and manipulating numerical data (with a bonus that when used correctly, it's waaaay faster than using Python lists). In addition, for dealing with tabular data with mixed datatypes, I recommend using pandas .

import pandas as pd
df = pd.load_csv('a.dat', sep=' ', names=['col1', 'col2'])
print df['col1']

Numpy can be found here

Pandas can be found here

Answer 2

This is wrong: a1 = array[:,1] putting values separated with comma make it a Tuple of 2 values. You should use:

a1 = array[0]

To get first row or to get first column use:

column = [row[0] for row in array]