Creating a list of tuples

Question

I am a given an input file with values of data to read from, the data is given in a pair of numbers like: (1, 2), (3, 4), (3, 5), (4,9) ..etc.

I must read each of these lines and make each line into a tuple and store the tuples in a list.

So far my code to do this is

def main():
tuples_list = []
    for item in sys.stdin:
        item = tuple(item)
        tuples_list = tuples_list.append(item)

However I have to ignore the first number in the input file and I am confused on how to modify my code to only start storing the values after that

Answer 1

No, this wont work. You shouldnt do a = a.append(b), just a.append(b). This works:

# file '1.py'
import sys

def main():
    tuples_list = []
    for item in sys.stdin:
        item = tuple(item)
        tuples_list.append(item)
    print(tuples_list)
main()

#file 'inp.txt'
1 2 3 4 
1 2 4 3
3 3 3 3

$ python 1.py <inp 
[('1', ' ', '2', ' ', '3', ' ', '4', ' ', '\n'), ('1', ' ', '2', ' ', '4', ' ', '3', '\n'), ('3', ' ', '3', ' ', '3', ' ', '3', '\n')]

But, in my opinion, using self-written procedures for file input is a bad idea. As you can see, this code reads characters, not numbers, so you need to fix it manualy, which leads to more code, with bugs, of course, debugging, waste of time, etc. You may want to do instead something like this:

# file inp.txt
1,2
3,4
5,6

import numpy as np
data = np.genfromtxt("inp.txt", delimiter=",")
print(data)

This will give you:

array([[1., 2.],
       [3., 4.],
       [5., 6.]])

This code is way faster than anything you will write(no, see comments below), because it uses numpy functions written in C/Fortran, way simpler to read, it handles any number of digits in line, and need no debugging. Using libraries are often better solution then writing code by yourself.

Answer 2

Assuming your input file looks something like this:

import sys

def main():
    num = sys.stdin.readline()

    # Removing parantheses
    num = num.replace('(', '').replace(')', '')

    # creating list from input
    ls = [int(x) for x in num.split(',')]

    # Sublisting current list to form list of tuples
    sub = []
    tuples_ls = []

    for i in ls:
        sub += [i]
        
        if len(sub) == 2:
            tuples_ls.append(tuple(sub))
            sub = []

    return tuples_ls