Polynomial Through Points

import numpy as np
from numpy.linalg import inv
import sys
import math

#Gets a valid input an returns it as a list of tuples
def get_input():
    #The message that wil be displayed to the inputter
    print('Type \'exit\' to exit')
    input_message = 'Write you coordinates: '
    #The characters of the input to be replaced, and the characters they should be replaced with
    replace_chars = [(' ', ''), ('(', ''), (')', ' '), (',', ' ')]
    #Repeatedly gets the input, until it is valid
    while True:
        s = input(input_message)
        if (s.lower() == 'exit'):
            sys.exit()
        #Replaces the replace_chars with nothing (deletes them)
        for char_pair in replace_chars:
            s = s.replace(char_pair[0], char_pair[1])
        #Replaces the ',' that split the coordinates, with a space
        s = s.replace(',', ' ')
        #Splits the string into words
        s_list = s.split()

        #Is the input valid?
        is_valid = validate_if_float(s_list) and (len(s_list) % 2 == 0)
        #If yes, the function should return the input
        if (is_valid):
            #Initializes the result list
            result = []
            #Loops through the input list, with iterates of two
            for i in range(0, len(s_list), 2):
                #Appends a touple of the coordinate pair to the result list
                result.append((float(s_list[i]), float(s_list[i + 1])))
            return result

        input_message = 'That input is invalid. Try again: '


#Validates if string every entry of a list can be converted to a float
def validate_if_float(number_list):
    is_all_numbers = True
    for n in number_list:
        if not is_number(n):
            is_all_numbers = False
            break
    return is_all_numbers

def is_number(s):
    try:
        float(s)
        return True
    except ValueError:
        return False


def create_matrix (coordinates):
    matrix_list = []
    for i in range(len(coordinates)):
        matrix_list.append(list())
        for j in range(len(coordinates)):
            num = math.pow(coordinates[i][0], j)
            matrix_list[i].append(num)

    return np.matrix(matrix_list)

def create_vector (coordinates):
    vector_list = []
    for i in range(len(coordinates)):
        vector_list.append([coordinates[i][1]])

    return np.matrix(vector_list)

def calculate_coefficients (A, b):
    v = inv(A) * b
    return v

def main ():
    coordinates = get_input()
    A = create_matrix(coordinates)
    b = create_vector(coordinates)
    v = calculate_coefficients (A, b)

    formula = 'f(x) = '
    for i in range(len(v)):
        formula = formula + str(float(v[i][0])) + ' * x^' + str(i) + ' + '
    formula = formula[:len(formula)-3]

    print(formula)
    input()


main()