image_resize.py

import os

from PIL import Image


FILENAME = 'tux.png'


def get_image_data(filename):
    try:
        return Image.open(filename)
    except OSError as error:
        return error


def get_resize_value(width, height, ratio=0.5):
    new_width = round(width * ratio)
    new_height = round(height * ratio)
    return new_width, new_height


def resize_image(image_data, new_width, new_height):
    return image_data.resize((new_width, new_height), Image.ANTIALIAS)


def save_image(resized_image, original_file):
    filename, ext = os.path.splitext(original_file.filename)
    x_size, y_size = resized_image.size
    path_to_save = '{}_{}x{}{}'.format(filename, x_size, y_size, ext)

    try:
        resized_image.save(path_to_save, original_file.format)
    except OSError as error:
        return error


def main():
    img = get_image_data(FILENAME)
    img_width, img_height = img.size
    new_width, new_height = get_resize_value(img_width, img_height)
    resized_img = resize_image(img, new_width, new_height)
    error = save_image(resized_img, img)

    if isinstance(error, OSError):
        print("File save error: ", error.strerror)
        sys.exit(error.errno)


if __name__ == '__main__':
    main()