How to change a list of strings to a list of integers

Question

I'm writing a program that takes a user file (a list of numbers, in this case) and calculate the mean, median, and mode of the list. However, I'm having a lot of trouble figuring out how to convert the number strings into integers. When I try, I get the error: "Invalid literal for int() in base 10" and then the first number of my list. No matter what I try I can't seem to convert the list even though this is the solution I keep seeing. Because of this, when I sort my list, it does not sort in numerical order. My mode function also seems to not be working very well, and even after a few days I can't figure out why. I would attach the file but there doesn't seem to be a way to do that, sorry. Hopefully this is enough information to see what might be causing the issues.

def CalculateMode(numbers):
    dictionary = dict()
    for num in numbers:
        if num in dictionary:
            dictionary[num] = dictionary[num] + 1
        else:
            dictionary[num] = 1
        maximum = max(dictionary.values())
        for key in dictionary:
            if dictionary[key] == maximum:
                print("The mode is " + key + ".")

def Main():
    openFile = open("testfile.txt", 'r')
    data = openFile.read()
    numbers = data.split()
    for num in numbers:
        num = int(num)
        return num
    numbers = sorted(numbers)
    print(numbers)
    while True:
        choice = input("Calculate Mode [1]  Exit [2]: ")
        if choice == "1":
            CalculateMode(numbers)
        elif choice == "2":
            break
        else:
            print("Please choose one of the above options.")

Main()

Answer 1

One option using as much of your code as possible is the following.

Note: Renamed variables to following the Python convention Pep 8 which is:

Function names should be lowercase, with words separated by underscores as necessary to improve readability.

Variable names follow the same convention as function names.

Code

import re

def calculate_mode(numbers):
    dictionary = dict()
    for num in numbers:
        if num in dictionary:
            dictionary[num] = dictionary[num] + 1
        else:
            dictionary[num] = 1

    maximum = max(dictionary.values())

    for key in dictionary:
        if dictionary[key] == maximum:
            print(f"The mode is {key}.")

def main():
    with open("testfile.txt", 'r') as open_file:
      # Extract consecutive digits using regex 
      # (see https://www.geeksforgeeks.org/python-extract-numbers-from-string/)
      data = re.findall(r"\d+", open_file.read())

      # Convert digits to integer
      numbers = [int(x) for x in data]

    # Sort numbers (inplace)
    numbers.sort()

    print(numbers)
    while True:
        choice = input("Calculate Mode [1]  Exit [2]: ")
        if choice == "1":
            calculate_mode(numbers)
        elif choice == "2":
            break
        else:
            print("Please choose one of the above options.")


main()

Input File (testfile.txt)

2, 3, 4, 5,
7, 9, 3, 2
1, 2, 9, 5
4, 2, 1, 8
6, 3, 4, 5

Output

[1, 1, 2, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 6, 7, 8, 9, 9]
Calculate Mode [1]  Exit [2]: 1
The mode is 2.
Calculate Mode [1]  Exit [2]:

Answer 2

Try cast using int(float(desired_string))

The string you're trying to cast is not convertible to int.

Edit: As gold_cy said, there is a logical inconsistency in your code that goes beyond the error presented.