def replace_placeholders(str, placeHolder, replacement):
    """
    Replace all the occurences of a substring in a string.

    Parameters
    ----------
        str (str): The string to be modified.
        placeHolder (str): The substring to replace.
        replacement (str): The replacement for the substring.

    Returns
    -------
        str (str): The new string with the substrings replaced.
    """
    return str.replace(placeHolder, replacement)