from typing import Tuple


def calculate_number_of_valid_lines(lines: Tuple[str]) -> int:
    """
    Note that this function does not count empty lines and headings.
    :param lines: Result of a f.readlines() operation, i.e., a list of strings.
    :return: The number of valid lines in this file
    """
    line_counter = 0
    for line in lines:
        if line.strip("\n ") and not line.startswith("=="):
            line_counter += 1
    return line_counter