Parses the command line and returns a ``Namespace`` object
    containing options and their values.

    :return:
        A ``Namespace`` object containing options and their values.

def parse_command_line():
    """
    Parses the command line and returns a ``Namespace`` object
    containing options and their values.

    :return:
        A ``Namespace`` object containing options and their values.
    """

    import argparse

    parser = argparse.ArgumentParser(description=__doc__.split("\n")[0])
    parser.add_argument('-v',
                        '--version',
                        action='version',
                        version='%(prog)s ' + __version__,
                        help="Show version number and exit.")
    parser.add_argument('input_filename',
                        metavar='INPUT_FILE',
                        type=str,
                        help='Path of the input file to be preprocessed')
    parser.add_argument('-q',
                        '--quiet',
                        dest='should_be_quiet',
                        action='store_true',
                        default=False,
                        help="Disables verbose logging")
    parser.add_argument('-L',
                        '--log-level',
                        '--logging-level',
                        dest='logging_level',
                        choices=[
                            'DEBUG',
                            'INFO',
                            'WARNING',
                            'ERROR',
                            'CRITICAL',
                            'NONE',
                            ],
                        default='INFO',
                        help="Logging level.")
    parser.add_argument('-o',
                        '--output',
                        metavar="OUTPUT_FILE",
                        dest='output_filename',
                        default=None,
                        help='Output file name (default STDOUT)')
    parser.add_argument('-f',
                        '--force',
                        dest='should_force_overwrite',
                        action='store_true',
                        default=False,
                        help='Force overwrite existing output file.')
    parser.add_argument('-D',
                        '--define',
                        metavar="EXPR",
                        dest='definitions',
                        action='append',
                        help="""\
Define a variable for preprocessing. <define>
can simply be a variable name (in which case it
will be true) or it can be of the form
<var>=<val>. An attempt will be made to convert
<val> to an integer so -D 'FOO=0' will create a
false value.""")
    parser.add_argument('-I',
                        '--include',
                        metavar="DIR_PATH",
                        dest='include_paths',
                        action='append',
                        default=['.'],
                        help='Add a directory to the include path for #include directives.')
    parser.add_argument('-k',
                        '--keep-lines',
                        dest='should_keep_lines',
                        action='store_true',
                        default=False,
                        help='''\
Emit empty lines for preprocessor statement
lines and skipped output lines. This allows line
numbers to stay constant.''')
    parser.add_argument('-s',
                        '--substitute',
                        dest='should_substitute',
                        action='store_true',
                        default=False,
                        help='''\
Substitute #defines into emitted lines.
(Disabled by default to avoid polluting strings)''')
    parser.add_argument('--default-content-type',
                        metavar="CONTENT_TYPE",
                        dest='default_content_type',
                        default=None,
                        help='If the content type of the file cannot be determined this will be used. (Default: an error is raised)')
    parser.add_argument('-c',
                        '--content-types-path',
                        '--content-types-config',
                        metavar="PATH",
                        dest='content_types_config_files',
                        default=[],
                        action='append',
                        help="""\
Specify a path to a content.types file to assist
with file type determination. Use the -p or -P flags
to display content types as read by pepe.""")
    parser.add_argument('-p',
                        '--print-content-types',
                        dest='should_print_content_types',
                        action='store_true',
                        default=False,
                        help='Display content types and exit.')
    parser.add_argument('-P',
                        '--print-content-types-config',
                        dest='should_print_content_types_config',
                        action='store_true',
                        default=False,
                        help='Display content types configuration and exit.')
    return parser.parse_args()